Fuel injector

Abstract

Injector (1) for direct fuel injection 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), - a supply connection (12) - a support (50) permanently fixed to the body (3) of the injector (1), and - a cup-shaped element (60) integral with the lower pin (6) and configured to provide a limit switch for the lower pin (6), predetermining a stroke value, maximum (C).

Description

[0001] FUEL INIECTOR

[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 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 (petrol, diesel, and gas) suffer from needle bounce, resulting in re-opening and post-injections, where post-injections are defined as unwanted injections that occur after the injector has been closed for a short time. These effects are caused by the dynamic behavior of the injector, and many features are designed to mitigate this effect, which is harmful to the engine. One example is the decoupling of the armature and needle to reduce impact energy.

[0011] The dynamic behavior of injectors is also characterized by extremely rapid transients that generate bounces and impacts of the moving components within the injector. This high-speed operation can induce complex interactions between components, which must be carefully managed to ensure optimal performance and injector longevity.

[0012] When the armature and needle are decoupled, several side effects occur. One such effect is overshooting, in which the needle travels beyond the armature's intended position. This misalignment can lead to incorrect fuel delivery, which impacts engine performance and efficiency. Another significant issue is post-injection, in which the injector reopens after a delay due to residual energy and impacts not fully dissipated within the injector. This inadvertent reopening can cause inconsistencies in fuel injection timing and quantity, resulting in variations in engine power output and increased emissions.

[0013] In many well-known applications, the moving armature of the electromagnetic actuator of injectors is coated with a hard material (e.g., chromium-based) to create a non-magnetic air gap between the armature and the ferromagnetic core and prevent magnetic sticking. The hard coating also serves as an impact surface that resists impact wear. This solution works well for injectors using gasoline or other liquid fuels that dampen impact energy. Thus, the hard coating serves the dual function of both a non-magnetic air gap and impact wear mitigation: first, it creates a nonmagnetic air gap, essential for the proper magnetic operation of the injector. Second, the hard coating acts as an impact surface, absorbing impact energy and defining the injector stroke. Stroke is a critical parameter that influences the amount of fuel injected into the combustion chamber. However, traditional hard coatings such as chromium present challenges, especially in the absence of a liquid fuel, as in gas injectors. Without a liquid to lubricate and cool the components, these coatings are prone to flaking and cracking under the mechanical stresses and thermal cycles experienced during operation. This degradation can lead to injector failure and compromise engine performance.

[0014] There is therefore a need to design a gas injector that eliminates, or at least minimizes, the aforementioned drawbacks.

[0015] Summary of the Invention

[0016] To substantially solve the technical problems highlighted above, an object of the present invention is to define a gas injector in which the problem of overshooting is solved and the need for hard coatings on the armature is eliminated.

[0017] 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.

[0018] Further embodiments of the invention, preferred and / or particularly advantageous, are described according to the characteristics set forth in the dependent claims attached.

[0019] Brief Description of the Drawings

[0020] The invention will now be described with reference to the accompanying drawings, which illustrate some non-limiting embodiments, in which:

[0021] - Figure 1 is a cross-section of a gas injector according to a preferred embodiment of the present invention, and

[0022] - Figure 2 illustrates, on an enlarged scale, a detail 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.

[0025] The fuel injector 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. However, this injector solution is also suitable for the injection of liquid fuels, such as liquid natural gas, ammonia, or methanol. 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.

[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 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.

[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 provided with openings for the passage of gas from the injector to the combustion chamber,

[0031] - 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.

[0032] 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.

[0033] 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

[0034] 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 solenoid

[0035] 8 and to a collar 11, distal to solenoid 8, which serves as an axial guide for armature 9. Armature 9 is integral with upper needle 6 and, in nonoperating conditions, abuts against a stop element 13.

[0036] The movable element is actuated to initiate a gas injection phase. As 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.

[0037] 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 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 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.

[0038] The combustible 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 area where the seal is established between the lower needle 6 and the nozzle 4 and, when the injector opens, the area of the nozzle 4 openings.

[0039] 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 gasket 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] 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.

[0042] 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 of bellows 17 generates a force in the closing direction of the injector.

[0043] The use of bellows 17 in combination with elastomer gasket 14 allows the gasket to have constant compression determined solely by the preload of elastic element 10. Otherwise, gasket compression would also depend on internal gas pressure, resulting in variable injector behavior as 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, the cup-shaped element 60, containing elastic element 10, is configured to provide a stroke limit for the lower needle 6. The cup-shaped element 60 comprises:

[0045] - a distal annular portion 61, integrally attached to the lower needle 6, for example, welded; and

[0046] - a flange portion 62 that extends proximally and is provided with an annular surface 63 at its end.

[0047] The support 50, integral with the lower body 3 and on which the elastic element 10 rests, also has a flange portion 52 that extends distally and is provided with an annular surface 53 at its end.

[0048] When the lower needle 6 opens, which, it should be remembered, moves proximally toward the combustion chamber, the cup element 60 provides a stop for the pin by stopping the cup element 60 against the support 50. More precisely, the annular surface 63 of the flange portion 62 of the cup element 60 comes into contact with the annular surface 53 of the support 50, thus defining a maximum stroke value C, i.e., the maximum value of the mechanical stroke of the lower needle 6. This solution is really simple and allows for optical measurement, the value of the maximum stroke C with a direct measurement.

[0049] With this solution, therefore, the maximum stroke C of the needle is independent of the magnetic air gap T. In known solutions, in fact, the magnetic air gap T, or the stroke that the armature 9 completes until it stops against the ferromagnetic core 7, also determines the value of the mechanical stroke of the needle, which therefore coincides with the magnetic stroke.

[0050] In this solution, however, it is possible to set a value for the maximum stroke C of the needle that is different and, in particular, smaller than the value of the magnetic air gap T.

[0051] By operating in this way, the maximum stroke C of the needle has a predetermined value, compatible with the characteristics of the injection to be achieved, and the cup element 60 provides the mechanical stop so that this maximum stroke value is not exceeded, i.e., there are no "overshooting" phenomena. Furthermore, the magnetic air gap T, which provides the required level of magnetic force, also has a predetermined value independent of the maximum stroke value C. Since the magnetic air gap T is larger than the maximum stroke value C, the armature 9 of the electromagnetic actuator 20, integral with the moving element 5, 6, never touches the ferromagnetic core 7, thus making the hard coating of the armature 9 unnecessary. Therefore, the residual air gap (T-C) at the end of the pin's maximum stroke is no longer determined by the thickness of the hard coating on the armature 9 but is simply an air gap.

[0052] Preferably, the T-C difference will be between 10 pm and 30 pm. A value less than 10 pm would result in a maximum stroke value C that is still too high: the pin would reach the end of its stroke with considerable impact velocities, and the risk of rebound would not be eliminated. Conversely, a T - C difference greater than 30 pm would determine a residual air gap that is too large and, consequently, an insufficient magnetic force.

[0053] Ultimately, the present invention solves the technical problem of overshooting of the injector's moving element.

[0054] The main advantages of the proposed solution include:

[0055] - increased injector life thanks to the avoidance of hard coatings such as magnetic circuit air gaps,

[0056] - ease of manufacturing and assembly: the use of the stroke stop element simplifies the stroke setting process and the subsequent control measurement,

[0057] - no risk of overshooting: the stop element prevents any overshooting of the maximum stroke because it creates a rigid mechanical stop that prevents any possible overshooting of the maximum stroke.

[0058] 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 a fuel direct injection 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 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),- a supply connection (12) the injector (1) being characterized in that it comprises:- a support (50) stably fixed to the body (3) of the injector (1), and- a cup-shaped element (60) integral with the lower needle (6) and configured to provide a lift stopper for the lower needle (6), predetermining a maximum lift (C) value.

2. Injector (1) according to claim 1, wherein the actuator (20) comprises a stationary ferromagnetic core (7) and an armature (9) axially movable together with the movable element (5, 6), wherein the ferromagnetic core (7) and the armature (9) define a magnetic air gap (T) in the axial direction, the magnetic air gap (T) being greater than the maximum lift (C).

3. Injector according to claim 2, wherein the difference between the magnetic air gap (T) and the maximum lift (C) is included in a range between 10 pirn and 30 pirn.

4. Injector according to any one of the preceding claims, wherein the cup element (60) comprises:- an annular portion (61), distal, integrally fixed to the lower needle (6), and- a flange portion (62) which protrudes in a proximal direction and at its end is provided with an annular surface (63).

5. Injector according to any one of the preceding claims, wherein the support (50) has a flange portion (52) which protrudes in a distal direction and at its end is provided with an annular surface (53).

6. Injector according to claims 4 and 5, wherein, the maximum lift (C) of the lower needle (6) is determined by the contact between the annular surface (63) of the flange portion (62) of the cup-shaped element (60) with the annular surface (53) of the support (50).

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

8. Injector (1) according to claim 7, wherein the gaseous fuel is hydrogen.

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