Low-pressure fuel injector

Abstract

Low-pressure fuel injector (1), the injector having: - a body (3), - a fuel connection (12), - a base (4), provided with an opening (4a) passing through in an axial direction for the fuel to escape - a movable element (5) of the injector (1), sealed against the base (4) when there is no injection, and configured to open inward by axial sliding when there is fuel injection, - an elastic calibration element (9), - a first ferromagnetic core (6), stably fixed to the body (3) of the injector and radially internal to the body itself, and - a second ferromagnetic core (7), sliding axially, wherein the movable element (5) is provided with a distal annular surface (5a), which defines, when there is no injection, a first air gap (H1) with an annular surface (7c) proximal of the second ferromagnetic core (7) and a second air gap (Htot) with an annular surface (6a) proximal of the first ferromagnetic core (6), where Htot > H1.

Description

[0001] LOW-PRESSURE 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 low-pressure fuel injector for application on internal combustion engines. The injector is particularly suitable for use with gaseous fuels and, even more particularly, is suitable for use with hydrogen.

[0005] Background art

[0006] Fuel injectors for internal combustion engines are well-known components in the field of internal combustion engine fuel systems. These injectors are typically operated by an electromagnetic actuator, using a solenoid that can be electrically energized to generate a magnetic field. This magnetic field induces the movement of a magnetic armature, which is typically connected to an opening element or needle of an 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 beginning of the opening of the nozzle orifice during the injection process is regulated by a spring element (e.g., a coil spring) positioned inside the fuel injector. This spring pushes the needle toward the nozzle orifice, meaning that the armature must counteract the spring force to open the nozzle orifice. Once the nozzle orifice is opened, a specified amount of gas inside the injector can flow into a combustion chamber, typically found in an internal combustion engine.

[0008] In the case of inward-opening 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 close the valve needle from the nozzle orifice.

[0009] Gas injectors, in particular, require high static flow rates due to the lower volumetric energy density of gas compared to liquid fuels. This introduces several design challenges. The requirement for larger flow crosssections and overall dimensions, unlike liquid fuel injectors, complicates their integration into the internal combustion engine.

[0010] Managing high gas flow rates further complicates the problem. The larger injector size increases the complexity of injector design, due to the requirement for a high flow rate, which affects injector performance.

[0011] The operating pressure range of gas injectors introduces additional challenges. Specifically, a wider flow path generates a significant difference in pneumatic forces between maximum and minimum pressures. This, combined with the high flow rate, requires a solenoid capable of generating a large magnetic force. This often limits the operating pressure range of these injectors and requires a more powerful drive current at lower pressures, complicating the design and requiring a larger solenoid diameter. This creates additional challenges for retrofitting these injectors.

[0012] Additionally, the required amount of magnetic force causes the armature to accelerate very rapidly, resulting in high-velocity impacts between the armature and the solenoid's ferromagnetic core. The consequences of this high velocity are:

[0013] - accelerated wear of the contact surfaces between these components;

[0014] - rebound of the armature (and consequently of the needle) against the ferromagnetic core. This causes an unwanted resumption of injection.

[0015] Currently, the wear problem is addressed by coating the contact surfaces of the two components with a hard surface coating, while reducing the rebound effect requires a special setting for the electromagnetic actuator control. Both of these measures, however, introduce design complications and increase injector costs.

[0016] Therefore, there is a need to design a low-pressure fuel injector, particularly a gas injector, that eliminates or at least minimizes the aforementioned drawbacks.

[0017] Summary of the Invention

[0018] To substantially solve the technical problems highlighted above, one object of the present invention is to define a low-pressure fuel injector, particularly a gas injector and, more specifically, a hydrogen injector, whose electromagnetic actuator is equipped with two ferromagnetic cores, one stationary and the other axially sliding.

[0019] By appropriately positioning these two elements, the armature stroke is divided into two parts, resulting in a substantial reduction in the impact velocities against the surfaces of the two ferromagnetic cores.

[0020] Therefore, according to the present invention, a low-pressure fuel injector is provided having the characteristics set forth in the independent claim, attached to the present description. Further embodiments of the invention, preferred and / or particularly advantageous, are described according to the characteristics set forth in the dependent claims attached.

[0021] Brief Description of the Drawings

[0022] The invention will now be described with reference to the accompanying drawings, which illustrate some non-limiting embodiments, in which:

[0023] - Figure 1 is a cross-section of an injector according to a preferred embodiment of the invention;

[0024] - Figure 2 shows, on an enlarged scale, a detail of the injector shown in Figure 1 in a first operating condition;

[0025] - Figure 3 shows, on an enlarged scale, a detail of the injector shown in Figure 1 in a second operating condition; and

[0026] - Figure 4 shows, on an enlarged scale, a detail of the injector shown in Figure 1 in a third operating condition.

[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 subject of the present invention is a low-pressure fuel injector, particularly suitable for use with gaseous fuels and therefore, hereinafter, will be referred to as a gas injector. As will be seen from the following description, the same injector can, however, be used for the injection of gaseous fuel, such as natural gas or hydrogen, but also for the injection of liquid fuels, such as liquefied natural gas, ammonia, methanol, and the like. The injector is suitable for internal combustion engines powered by gas by means of indirect injection (or PFI, from the English Port Fuel Injection), in which the fuel gas is injected into the intake duct of each cylinder upstream of the corresponding intake valve.

[0029] With reference to Figure 1, injector 1 is an indirect injection gas injector that injects gaseous fuel into a known intake duct (not shown in the figures) of an internal combustion engine. The intake duct and the internal combustion engine are not part of the present invention.

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

[0031] Injector 1 has a modular design that includes a power unit 10 and a valve unit 20.

[0032] Power unit 10 is an electromagnetic or piezoelectric actuator. In the embodiment illustrated in the figures, the power unit is an electromagnetic actuator and comprises:

[0033] - a distal casing 2, substantially hollow cylindrical in shape and with a cross-section shaped like two opposing "C"s, onto which an electrical connector (of a known type and therefore not shown in the figure) is comolded in a known manner for the power unit's electrical supply,

[0034] - a solenoid 8, hollow cylindrical, mounted integrally inside casing 2,

[0035] - a first ferromagnetic core 6, hollow cylindrical and stationary, housed inside casing 2 and solenoid 8, stably attached to an injector body 3 and radially internal to the body itself,

[0036] - a second ferromagnetic core 7, axially slidable, also hollow cylindrical but with a cross-section shaped like two inverted and opposing "L"s. The webs 7a of the L-shaped sections, radially internal to the first ferromagnetic core 6, are protruding and more proximal to the first ferromagnetic core 6. When the injector is closed, the flanges 7b of the two L-shaped sections of the second ferromagnetic core 7 are pressed onto the first ferromagnetic core 6 by the spring force produced by an elastic element 11, for example, a helical spring as shown in the figures, and

[0037] - a movable armature 5, proximal to the first 6 and the second ferromagnetic core 7 and axially sliding. The movable armature 5 comprises a distal annular surface 5a, which defines, in closed injector conditions, a first air gap Hl (or distance) with an annular surface 7c of the second ferromagnetic core 7 and a second air gap Htot (or total air gap or distance) with an annular surface 6a of the first ferromagnetic core 6. Evidently, for the geometry of the two ferromagnetic cores 6, 7 described above, the result must be: Htot > Hl.

[0038] In the following, the terms air gap and distance will be used interchangeably depending on the context.

[0039] The valve assembly 20 comprises:

[0040] - the body 3 of the injector 1, of a substantially hollow cylindrical shape, integrally connected to the casing 2 and containing the two ferromagnetic cores 6, 7 and the armature 5,

[0041] - a supply connection 12 for the gas supply to the injector 1, permanently fixed to the body 3. In Figure 1, the supply connection is located distal to the body 3, and this type of supply is known as "top feed." In other embodiments, the gas supply can be achieved through openings along the lateral surface of the body 3, generally known as "bottom feed",

[0042] - a disc 4, integrally positioned with the proximal end of the body 3 and equipped with an opening 4a passing axially from the injector to the intake duct,

[0043] - a movable element 5 of the injector, or needle, configured to open inward. The needle 5 coincides with the movable armature 5 of the power unit 10, and therefore, hereinafter, the terms "movable element," "armature," or "needle" will be used interchangeably depending on the context.

[0044] During the opening of the injector 1, the needle 5 assumes a more distal position with respect to the intake duct. The injector's hermetic seal against the passage of gas flow is achieved by a seal between the needle 5 and the disc 4, ensured by the spring force of an elastic calibration element 9, again by way of example, a helical spring. The spring 9 is radially internal with respect to the second ferromagnetic core 7 and rests on a spacer 13, radially internal and integrally connected to the second ferromagnetic core 7 itself.

[0045] The needle 5 is actuated by the power unit 10 to initiate a gas injection phase by its axial movement towards positions more distal with respect to the intake duct. This allows the gas to flow into the intake duct.

[0046] To terminate an injection, simply de-energize the power unit 10 and the needle 5 returns to its sealing position on the disc 4 thanks to the spring force exerted by the helical spring 9. According to the present invention, the solution adopted to reduce the speed of the armature 5 is to define a ferromagnetic core in two elements, namely the first ferromagnetic core 6 and the second ferromagnetic core 7.

[0047] With reference to Figure 2, which illustrates the detail of the power unit 10 in the closed injector configuration (no injection), the advantage of this solution is given by the fact that the distance Hl (i.e. the initial air gap Hl) between the annular surface 5a of the armature 5 and the annular surface 7c of the second ferromagnetic core 7 is less than the distance Htot between the annular surface 5a of the armature 5 and the annular surface 6a of the first ferromagnetic core 6. The distance Htot (i.e. the air gap Htot) represents the travel that the armature, i.e. the needle 5, must complete to guarantee the gas injection flow rate required by the specific application.

[0048] With reference to Figure 3, once the power unit 10 is energized, the armature 5 begins to move, due to the magnetic force that develops mainly through the second air gap Hl (smaller than the first air gap Htot), until it reaches the second ferromagnetic core 7, having traveled the distance Hl. In this intermediate operating condition (Figure 3), the annular surface 5a of the armature 5 is in contact with the annular surface 7c of the second ferromagnetic core 7. The size of the distance Hl, which is smaller than that necessary for the total required flow rate, requires a lower magnetic force to initiate the opening of the injector. This lower magnetic force results in a reduced acceleration of the armature 5, which, in combination with the distance travel Hl (shorter than the distance Htot), determines a lower impact velocity and, therefore, a less stressful impact. At this stage, the magnetic force will overcome the spring force of the calibration spring 9 and the pressure force exerted by the gas. Once contact is achieved with the second ferromagnetic core 7, the armature will feel attracted to the first ferromagnetic core 6 due to the magnetic force now developing across the air gap between the latter components, an air gap that will no longer be equal to Htot but will have reduced to the value H2=Htot-Hl. The magnetic force that develops, also with the aid of the momentum of the armature 5 and the small residual distance H2 between the armature itself and the first ferromagnetic core 6, must overcome the resistance given by the gas pressure force and the spring force exerted by the spring 11 on the first ferromagnetic core 6. In particular, the spring force of the spring 11 must be such as to slow the speed of the armature so that the impact force with the first ferromagnetic core 6 is within the required limits. In this phase, therefore, armature 5, second ferromagnetic core 7, calibration spring 9 and spacer 13 will move as a single rigid body.

[0049] Referring to Figure 4, the operating condition of the injector's maximum opening can be observed. This condition is the one that guarantees the required gas flow rate, with armature 5 having traveled the entire distance Htot and its annular surface 5a being in contact with the annular surface 6a of the first ferromagnetic core 6. The useful result is that armature 5 travels the entire distance Htot in two phases, during each of which it is subjected to smaller accelerations than it would have if it had traveled the entire distance in the face of a significantly greater magnetic force.

[0050] It should be noted that during the first phase, the second ferromagnetic core 7 must not move, otherwise the idea of operating with two smaller air gaps, Hl and H2, compared to the required air gap Htot would be nullified. To meet this condition, the following must be true:

[0051] F9 < Fll where:

[0052] F9 is the spring force of the calibration spring 9, and

[0053] Fll is the spring force of the spring 11.

[0054] Conveniently, the second air gap Hl should be neither too small nor too close to the first air gap Htot, so as not to lose the beneficial effects of operating with two smaller air gaps, Hl and H2, compared to the air gap Htot. Preferably, the second air gap Hl can be between 20% and 50% of the first air gap Htot.

[0055] Ultimately, the present invention achieves the following advantages:

[0056] - reduced wear between the impact surfaces of the armature and the ferromagnetic cores due to the reduced speed of the armature, thus eliminating the need for expensive hard surface coatings;

[0057] - absence of reopening of the pin and, therefore, of unwanted injections, due to the lack of rebound of the armature upon impact with the ferromagnetic cores.

[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. Low-pressure fuel injector (1) for indirect injection of fuel into an intake manifold of an internal combustion engine, the injector comprising:- a body (3) of hollow cylindrical shape,- a supply connection (12) for the fuel supply to the injector (1), stably fixed to the body (3),- a disc (4), integrally positioned at the proximal end of the body (3) and provided with an opening (4a) passing, in an axial direction, for the fuel to flow out of the injector to the intake manifold,- a mobile element (5) of the injector (1) sealed on the disc (4), in conditions of non-injection, and configured to open inwards, by axial sliding, in conditions of fuel injection,- a power unit (10) for the actuation of the mobile element (5),- a first elastic element (9) for calibration, to ensure the seal of the mobile element (5) on the disc (4) in conditions of non-injection, wherein the power unit (10) comprises:- a first ferromagnetic core (6), stably fixed to the body (3) of the injector and radially internal to the body itself, and- a second ferromagnetic core (7), axially sliding, wherein the mobile element (5) comprises a distal annular surface (5a), which defines, in conditions of non-injection, a first air gap (Hl) with an annular surface (7c) proximal to the second ferromagnetic core (7) and a second air gap (Htot) with an annular surface (6a) proximal to the first ferromagnetic core (6), wherein Htot > Hlthe injector (1) being characterized in that the second ferromagnetic core (7) has a cross-section in the shape of two inverted and opposite "L" and, in conditions of non-injection, the webs (7a) of the "L" sections, radially internal to the first ferromagnetic core (6), are protruding and more proximal with respect to the same first ferromagnetic core (6).

2. Injector (1) according to claim 1, wherein, in conditions of noninjection, the wings (7b) of the two "L" sections of the second ferromagnetic core (7) are pressed onto the first ferromagnetic core (6) by the effect of the elastic force produced by a second elastic element (11).

3. Injector (1) according to claim 2, wherein the elastic force (F9) of the first elastic element (9) is less than the elastic force (Fl 1) of the second elastic element (11).

4. Injector according to any one of the preceding claims, wherein the first air gap (Hl) is between 20% and 50% of the second air gap (Htot).

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

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

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