Low pressure fuel injector

Abstract

A low pressure fuel injector (1) for indirect injection of fuel into an intake manifold of an internal combustion engine, the injector having: - a body (3), - at least one opening (12), passing, along the lateral surface of the body (3) for the supply of fuel to the injector (1), - a disc (4) provided with an opening (4a), passing, in an axial direction, for the exit of fuel, - a movable element or armature (6) 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 operation of the armature (6), comprising at least the ferromagnetic core (7), - an elastic calibration element (9), to ensure the seal of the mobile element (6) on the disc (4) in conditions of absence of injection, wherein between a radially external cylindrical surface (6c) of the armature (6) and a radially internal cylindrical surface (3c) of the body (3) there is an annular meatus (g).

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 internal combustion engine applications. 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 toward more distal axial positions. This armature typically also functions as a moving element (or needle) of an injector nozzle or is connected to the moving element.

[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 (e.g., a coil spring) positioned 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 gas inside the injector can flow into the intake manifold (port fuel injection or PFI) and then 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] In particular, gas injectors 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. To best support high- flow gas PFI applications, a bottom-feed actuator / injector architecture is used to avoid additional flow restrictions in the design.

[0010] Managing high gas flow rates further complicates the problem. The larger size of the injector increases the complexity of injector design, due to the need 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 creates 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] In addition, an electromagnetic actuator requires a very large stroke to ensure flow through the valve. Stroke refers to the lift or elevation of the armature, or needle.

[0013] The combination of a large magnetic force and a large armature stroke causes a very high acceleration of the armature, resulting in high- velocity impacts (even exceeding 2 m / s) between the armature's impact surface and the corresponding impact surface of the actuator's ferromagnetic core. The consequences of this high impact velocity are:

[0014] - faster wear of the impact surfaces between these components;

[0015] - rebound of the armature (and consequently the needle) against the ferromagnetic core. This causes an unwanted re-injection.

[0016] Currently, wear is addressed by coating the impact surfaces of the two components with a hard surface coating, while rebound effects are reduced by special settings for the electromagnetic actuator and / or the use of viscoelastic damping solutions. However, all of these measures introduce design complications and increase injector costs.

[0017] In particular, hydrogen injectors often require high static flow rates, which further complicate injector design due to the relatively low density of hydrogen, especially in indirect injection applications (PFI with pressures varying between 5 and 15 bar). This introduces further complexities into injector design, such as the requirement for high lift (e.g., 500 pm or greater), which affects injector performance under dynamic conditions. Furthermore, the viscoelastic damping solution cannot fully guarantee both durability, mechanical stability, and accurate fuel metering.

[0018] The long stroke required to achieve the required volumetric flow of gaseous fuel increases the armature's momentum and kinetic energy. These parameters cannot be easily counteracted: first, as the armature's stroke increases and the resulting air gap between the ferromagnetic core and the armature decreases, a positive feedback loop is generated, further increasing the magnetic attraction force for the same excitation current, which further accelerates the armature. Second, there are severe limitations in the use of external parameters, such as the shape of the voltage and current profile: the magnetic field transient in a circuit where the magnetic conductive materials, such as stainless steel, are relatively long compared to the actuator's magnetization / demagnetization time.

[0019] There is therefore a need to define a low pressure fuel injector, particularly a gas injector, that avoids or at least minimizes the aforementioned drawbacks.

[0020] Summary of the Invention

[0021] To substantially solve the technical problems highlighted above, an object of the present invention is to define a low pressure fuel injector, particularly a gas injector, and, more specifically, a hydrogen injector, whose actuator is equipped with an automatic self-damping function that reduces the impact velocities of the armature on the ferromagnetic core.

[0022] Therefore, according to the present invention, a low pressure fuel injector is provided, the injector having the features set forth in the independent method claim, appended to this specification.

[0023] Further preferred and / or particularly advantageous embodiments of the invention are described according to the features set forth in the appended dependent claims.

[0024] Brief Description of the Drawings

[0025] The invention will now be described with reference to the accompanying drawings, which illustrate some non-limiting examples of its implementation, in which:

[0026] - Figure 1 is a cross-section of an injector according to a preferred embodiment of the invention;

[0027] - Figure 2 shows, in cross-section and on an enlarged scale, a detail of the injector shown in Figure 1;

[0028] - Figure 3 shows, in cross-section and on a further enlarged scale, the detail of the injector shown in Figure 1 in a first operating condition; and

[0029] - Figure 4 shows, in cross-section and on a further enlarged scale, the detail of the injector shown in Figure 1 in a second operating condition.

[0030] Detailed Description

[0031] 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 applications in the presence of 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 (PFI), in which the fuel gas is injected into the intake duct of each cylinder upstream of the corresponding intake valve.

[0032] With reference to Figures 1 and 2, injector 1 is an indirect injection gas injector that injects gaseous fuel into a known intake duct (not illustrated in the figures) of an internal combustion engine. The intake duct and the internal combustion engine are not part of the present invention.

[0033] 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.

[0034] Injector 1 has a modular design that includes a power unit 10 and a valve assembly 20.

[0035] The 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:

[0036] - a distal casing 2, of a substantially hollow cylindrical shape and with a cross-section in the shape of two opposing "C"s, onto which an electrical connector 11 for the power supply to the power unit is co-molded in a known manner,

[0037] - a hollow cylindrical solenoid 8, mounted integrally within the casing 2,

[0038] - a stationary cylindrical ferromagnetic core 7, provided with a radially internal through cavity 7'. The core 7 is housed inside the casing 2 and the solenoid 8, permanently attached to an injector body 3 and radially internal to the body itself, and

[0039] - a movable armature 6, proximal to the ferromagnetic core 7 and axially slidable. The armature 6 comprises a distal annular surface 6a, which, when the injector is closed, defines an air gap (or distance) with an annular surface 7a and proximal to the core 7.

[0040] Hereinafter, the terms air gap and distance will be used interchangeably depending on the context.

[0041] The valve assembly 20 comprises:

[0042] - the body 3 of the injector 1, of a substantially hollow cylindrical shape, integrally connected to the casing 2 and containing the ferromagnetic core 7 and the armature 6;

[0043] - at least one opening 12 passing along the lateral surface of the body 3 for the gas supply to the injector 1. This type of supply is generally known as "bottom feed." In another embodiment, not part of the present invention, the supply can be achieved by means of a supply connection distal to the body 3, a type of supply known as "top feed";

[0044] - a disc 4, integrally positioned at the proximal end of the body 3 and provided with at least one opening 4a passing axially for the gas to escape from the injector into the intake duct;

[0045] - a movable element 6 of the injector or needle configured to open inward. Preferably, the needle 6 coincides with the movable armature 6 of the power unit 10 and therefore in the following the terms movable element, armature or needle will be used interchangeably depending on the context. In other solutions, always forming part of the present invention, the needle and the armature may be two separate but integral components. During the opening of the injector 1, the needle 6 assumes a more distal position with respect to the intake duct. The hermetic closure of the injector as the gas flow passes is achieved by a seal 5 between the needle 6 and the disc 4, ensured by the spring force of an elastic calibration element 9, for example, a helical spring. The spring 9 is housed in the cavity 7' of the ferromagnetic core 7 and rests on an adjustment pin 13, also housed in the cavity 7' of the core 7 and integrally connected to the ferromagnetic core 7 itself.

[0046] The needle 6 is actuated by the power unit 10 to initiate a gas injection phase by its axial movement and towards positions more distal with respect to the intake duct. In this way, the gas can flow into the intake duct.

[0047] To terminate an injection, simply de-energize the power unit 10 and the needle 6 returns to its sealing position on the base 4 thanks to the spring force exerted by the helical spring 9.

[0048] With reference also to Figures 3 and 4, the present invention defines a damped impact solution for the armature moving toward the ferromagnetic core. To reduce the speed of armature 6 during the opening phase of injector 1, this solution, which we could define as self-damping, exploits the properties of the hydrogen or gas used and the internal geometries of the injector to reduce the armature speed by approximately an order of magnitude compared to the armature speed of a prior art injector.

[0049] Injector 1 has a "bottom feed" architecture, and armature 6 is designed such that between its radially external cylindrical surface 6c and a radially internal cylindrical surface 3c of body 3 there is an annular gap g whose radial dimension is a few microns and preferably between 3 pm and 5 pm. In this way, the fluid inside this gap behaves like a viscous fluid, so during the movement of armature 6, there will be only a small amount of fluid leakage. This fluid will pass from a volume V above armature 6 to a volume VI below it. Specifically, the volume V is defined as the sum of a first volume between the annular surface 6a of armature 6 and the annular surface 7a of the ferromagnetic core 7, and a second volume corresponding to the volume of the cavity 7' of the core 7, net of the volume of the adjustment pin 13 and the helical spring 9. The annular gap g could be produced using standard manufacturing technologies such as grinding or other equivalent processes, already used for injector components, to achieve very precise tolerances.

[0050] To achieve the desired effect during operation, as will be understood later, the volume V between armature 6 and ferromagnetic core 7 must be as small as possible. For this purpose, the adjustment pin 13 is provided with a proximal appendage 13', preferably cylindrical in shape, which, together with the spring 9, occupies a large portion of the cavity 7' of the ferromagnetic core 7, thus reducing the volume V.

[0051] During the time interval in which the armature 6 travels, the volume V will change from a maximum volume VO, when the armature / needle is still in the sealing position on the base 4 and the injector is closed (Figure 3), to a minimum volume Vf, when, with the injector open, the armature 6 has completed its entire travel (Figure 4).

[0052] In the initial condition, with the injector closed, the gas pressure is the same on the distal annular surface 6a of the armature and on an annular surface 6b, proximal to the armature itself. In other words, the gas pressure is the same in volume VO and volume VI, and the forces associated with the pressure are in equilibrium.

[0053] When the injector opens, armature 6 is activated by the magnetic force that overcomes the spring force of spring 9. The armature will begin its stroke, and the volume V will progressively decrease from a maximum value VO to a minimum value Vf. According to the fluid continuity equation and the ideal gas law (as a first approximation, the gaseous fuel can be considered a perfect gas and the thermodynamic process an adiabatic process), the reduction in volume V will lead to an increase in the gas pressure in volume V. The progressive increase in this pressure in volume

[0054] V (which is decreasing from VO to Vf) creates a dynamic pressure differential between the pressure in volume V and the pressure in volume VI. Consequently, a pressure force is created that opposes the magnetic force. This will result in a reduction in the velocity, momentum, and kinetic energy of armature 6. The dynamic behavior of this process is therefore balanced by the viscous and laminar flow of gas within the gap g between surface 6c of armature 6 and surface 3c of body 3.

[0055] Conversely, as the injector closes, the volume V will increase from the minimum value Vf to the maximum value VO. The pressure in volume

[0056] V will decrease until it balances with the pressure in volume VI. The spring force of spring 9 will therefore act on armature 6, along with a pressure differential (pressure in volume V - pressure in volume VI) that will tend to cancel out as the armature closes. Therefore, even during the closing phase, the motion of armature 6 is damped, resulting in a reduction in the speed, momentum, and kinetic energy.

[0057] The change in volume V from VO to Vf is defined as the Vf / VO ratio, which, depending on the application, preferably ranges between 40% and 60%. Higher percentages would result in insignificant damping of the armature motion, thus negating the effectiveness of this solution. Percentages lower than 40% could result in excessive damping of the anchor motion, potentially causing "elastic rebound," or a reversal of the armature motion.

[0058] In a preferred embodiment, VO is approximately 88 mm3 while Vf is approximately 45 mm3, resulting in a Vf / VO ratio of approximately 50%. For this embodiment, the applicant has performed careful modeling and simulations using computational fluid dynamics codes, demonstrating the armature's damping capacity. Different ratios between Vf and VO can be considered based on the injector application and the gas properties.

[0059] As can be seen, an important role in the present invention is played by the adjustment pin 13 and, in particular, its appendage 13'. The present solution can be optimized using the diameter and length of the appendage 13' as parameters. Furthermore, the shape of the appendage 13' can be cylindrical or prismatic, as well as featuring one or more axial grooves and / or one or more radial notches. These variations are useful for adapting the appendage 13' to the dimensions of the cavity 7' of the ferromagnetic core 7 and the helical spring 9.

[0060] Ultimately, the present invention defines an automatic self-damping function in an electromagnetic actuator of a gas injector that can be used as a stand-alone solution or in combination with strategies that act on the current profile to limit the armature speed.

[0061] The invention achieves the following advantages:

[0062] - reduced wear between the impact surfaces of the armature and the ferromagnetic core due to the reduced impact velocity of the armature, thus eliminating the need for expensive hard surface coatings;

[0063] - no needle reopening and, therefore, unwanted injections, due to the lack of rebound of the armature upon impact with the ferromagnetic core.

[0064] Furthermore, this solution also significantly improves actuator flow control during the reverse movement (injector closing transient). This selfdamping reduces the needle closing speed, thus extending the life of the seal on the end cap.

[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. A 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,- at least one opening (12), passing, along the lateral surface of the body (3) for the supply of fuel 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 exit of fuel from the injector to the intake manifold,- a movable element or armature (6) 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 operation of the armature (6), comprising at least the armature (6) and a ferromagnetic core (7),- an elastic calibration element (9), to ensure the seal of the mobile element (6) on the disc (4) in conditions of absence of injection, wherein between a radially external cylindrical surface (6c) of the armature (6) and a radially internal cylindrical surface (3c) of the body (3) there is an annular meatus (g), the injector being characterized in that:- a volume (V) is defined as the sum of a first volume included between a distal annular surface (6a) of the armature (6) and a proximal annular surface (7a) of the ferromagnetic core (7) and a second volumecorresponding to the volume of a radially internal cavity (7') passing through the core (7), net of the volume of the elastic element (9) and of a adjustment pin (13) of the elastic element (9), both housed in the cavity (7'),- the volume (V) varies from a maximum volume (VO) in the absence of injection to a minimum volume (Vf) in the presence of injection, and- the ratio between the minimum volume (Vf) and the maximum volume (VO) is between 40% and 60%.

2. Injector (1) according to claim 1, wherein the radial dimension of the annular meatus (g) is between 3 pirn and 5 pirn.

3. Injector according to claim 1 or 2, wherein the adjustment pin (13) is provided with a proximal appendage (13')-4. Injector according to claim 3, wherein the appendage (13') has a cylindrical shape.

5. Injector according to claim 3, wherein the appendage (13') has a prismatic shape.

6. Injector according to claim 4 or 5, wherein the appendage (13') has one or more axial grooves and / or one or more radial incisions.

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

8. Injector (1) according to anyone of the preceding claims, wherein the gaseous fuel is hydrogen.

Images