Low pressure fuel injector

Abstract

A low-pressure fuel injector (1) for indirect fuel injection into an intake duct of an internal combustion engine, the injector being provided with: - an upper body (2) and a lower body (3), in which the lower body (3) is provided with first (3a) and second through holes (3b) for the gas inlet inside the injector (1), - a cap (4, 40) provided with a plurality of openings (4a, 40a) passing fuel from the injector (1) to the intake duct, - a needle (5) configured to unlock and close the openings (4a, 40a) of the cap (4, 40) and to open towards the inside, and - an electromagnetic actuator (9) for actuating the closing element (5), the injector (1) also having a double fuel flow path in which the edges along the two paths are chamfered or radiused.

Description

[0001] LOW PRESSURE FUEL INJECTOR

[0002] DESCRIPTION

[0003] Technical Sector of the Invention

[0004] The present invention relates to a low-pressure fuel injector for application to internal combustion engines.

[0005] The injector is particularly suitable for use with fuels in the gaseous state and, even more particularly, is suitable for use with hydrogen.

[0006] Background art

[0007] Fuel injectors for internal combustion engines are known components in the field of fuel supply systems for internal combustion engines. Normally, the actuation of these injectors is electromagnetic, using a solenoid that can be energized electrically to generate a magnetic field. This magnetic field induces the movement of an armature made of magnetic material, which is generally connected to an opening element or needle of a nozzle of the injector, making it move along its axis.

[0008] The needle, moving in tandem with the armature, controls the opening or closing of the nozzle orifice on its tip. The start of the opening of the nozzle orifice during the injection process is regulated by an elastic element positioned inside the fuel injector. This spring pushes the needle towards the nozzle orifice, which means that the armature must counteract the force of the spring to open the nozzle orifice. Once the nozzle orifice is opened, a predetermined quantity of gas, inside the injector, can flow in a combustion chamber, typically present in an internal combustion engine. In the case of injectors with inward opening, the magnetic force must overcome not only the preload of the spring but also the pneumatic / hydraulic pressure acting on the surfaces wetted by the fuel, which helps to close the needle from the nozzle orifice.

[0009] Typically, fuel injectors internally retain the fluid when they are not actuated, by means of a metal-to-metal seal between two components or by means of an elastomeric material seal. A failure of this seal could cause a loss of fuel from the tip of the nozzle.

[0010] In particular, gas injectors require high static flow rates due to the lower volumetric energy density of the gas compared to liquid fuels. This introduces several design challenges. The need for larger flow sections and overall dimensions, unlike liquid fuel injectors, complicates their integration into an internal combustion engine. Sometimes two injectors per cylinder are combined with a lower flow rate instead of one injector with a higher flow rate. To accommodate two injectors or an injector of larger dimensions, modifications to the intake manifold of the internal combustion engine are often necessary.

[0011] The management of high gas flow rates further complicates the problem. The larger size of the injector increases the complexity in the design of the injector, due to the need for high lift that influences the performance of the injector.

[0012] The operating pressure range of gas injectors introduces further problems. Specifically, a wider flow path generates a significant difference in pneumatic forces between maximum and minimum pressures. This, in combination with the high lift, requires a solenoid capable of generating a large magnetic force. This often limits the operating pressure range of such injectors and requires a more powerful pilot current at lower pressures, complicating the design and requiring a larger solenoid diameter. Hence further problems for the retrofit of such injectors.

[0013] This often limits the operating pressure range of such injectors: a very high magnetic force at low pressures causes a too high impact force on the pintle; conversely, a magnetic force that is too low does not allow a rapid opening of the injector.

[0014] The large flow sections of the gas also imply large contact surfaces between components, thus reducing the contact pressure at equal overall force. This reduction in contact pressure compromises the effectiveness of meta I -to- meta I seals, especially because gas molecules can leak through the smallest imperfections.

[0015] Therefore, there is a need to define a low-pressure fuel injector, particularly a gas injector, that is free from or minimizes the aforementioned drawbacks.

[0016] Summary of the Invention

[0017] To substantially solve the technical problems mentioned above, one purpose of the present invention is to define a low-pressure fuel injector, particularly a gas injector, or even more particularly, a hydrogen injector, provided with a double path for the gas flow and a seal made of elastomeric material.

[0018] In this way, it is possible to obtain high static flow rates, in particular greater than 5 g / s for a pressure difference of 4.5 bar, a reduction of pneumatic forces between the maximum and minimum pressure, minimal injector dimensions comparable to known embodiments, for example, gasoline injectors, and the possibility of ensuring a good gas seal even at very low operating pressures.

[0019] 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.

[0020] 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 section of an injector according to the present invention,

[0024] - Figures 2 and 3 illustrate, on an enlarged scale and, respectively, in section and in an axonometric view, a detail of the injector of Figure 1 according to a first and preferred embodiment of the invention,

[0025] - Figures 4 and 5 illustrate, on an enlarged scale, a detail of the injector of Figure 1 in a second embodiment of the invention, and

[0026] - Figures 6 and 7 illustrate, on an enlarged scale, a detail of the injector of Figure 1 in a third embodiment of the invention.

[0027] Detailed Description

[0028] By way of purely exemplary and non-limiting example, the present invention will now be described with reference to the aforementioned figures.

[0029] The object of the present invention is a low-pressure fuel injector, particularly suitable for application in the presence of gaseous fuels and therefore, hereinafter, will be referred to as a gas injector. As can be seen from the following description, the same injector can, however, be used for the injection of gaseous fuel, for example, natural gas or hydrogen, but also for the injection of liquid fuels, for example, liquid 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.

[0030] With reference to Figure 1, the injector 1 is a gas injector for indirect injection that injects the fuel gas into an intake duct, of a known type and therefore 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.

[0031] Throughout the present description and in the claims, the terms and expressions indicating positions such as "proximal" and "distal" are intended to refer to the distance from the intake duct. Terms such as "radially internal" or "radially external" are intended to refer to an axis X of axial symmetry 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 provided with axial symmetry with respect to the axis X. The injector 1 has a modular design that includes a power group 10 and a valve group 20.

[0032] The power group 10 in turn comprises:

[0033] - an upper body 2, distal, substantially cylindrical in shape, hollow on which an electrical connector 2a is molded in a known manner for the electrical supply of the power group,

[0034] - a cap 12 that fluid-tightly closes the distal portion of the injector 1,

[0035] - an actuator 9 for actuating the valve group 2.

[0036] The valve group 20 in turn comprises:

[0037] - a lower body 3, proximal, also substantially cylindrical in shape, solidly connected to the upper body and provided with first 3a and second through holes 3b for the gas inlet inside the injector, in which the first through holes 3a have an internal diameter greater than the internal diameter of the second through holes 3b,

[0038] - a cap 4, solidly positioned at the proximal end of the lower body 3 and provided with a plurality of through openings 4a for the outflow of gas from the injector to the intake duct. The openings 4a extend in an axial direction,

[0039] - an injector closing element or needle 5 that is configured to open inwards. In other words, the needle 5 during the opening of the injector 1 assumes a more distal position with respect to the intake duct. The hermetic closure of the injector to the passage of gas is achieved by a sealing element between the needle 5 and the cap 4, as will be better explained below. The needle 5 has an axial cavity 5a shaped like a blind hole with a proximal opening with respect to the intake duct and in fluid communication with the first through holes 3a.

[0040] The needle 5 is actuated by the actuator 9, for example an electromagnetic actuator or a piezoelectric actuator. In the embodiment illustrated in Figure 1, the actuator 9 is an electromagnetic actuator and includes a ferromagnetic core 7, stationary, housed inside the lower body 3 and integral with it. A solenoid 8 is mounted integrally with the lower body 3, radially external to it but radially internal with respect to the upper body 2. Finally, the actuator 9 includes the needle 5 which also performs the function of a movable armature, radially internal with respect to the solenoid 8, and together with the electromagnetic core 7 defines a gap of amplitude p. More precisely, the gap axial amplitude p is the distance between the respective facing surfaces 5', 7' of the needle 5 and of the electromagnetic core 7. Therefore, the needle 5 assumes the dual function of closing element of the injector 1 and of movable armature of the electromagnetic actuator 9. The actuation of the mobile armature, i.e. of the needle 5, occurs to start a gas injection phase. As a result of its movement in an axial direction and towards more distal positions with respect to the intake duct, allowing the outflow of gas into the intake duct.

[0041] At the end of an injection, the injector closing element is restored in a known manner by means of an elastic element 11, for example a helical spring.

[0042] With reference to Figure 2, the valve group 20 defines the path of the fluid flow. When the power group 10 is activated, a magnetic force is generated and the injector 1 opens allowing the metering of the gaseous fluid. When the power group 10 is not activated, the spring 11 has the function of keeping the injector 1 closed allowing a tight contact between the pin 5 and the bottom 4.

[0043] The valve group 20 is provided with the supply gas inlet in a proximal position with respect to the intake duct. The gas inlet is obtained by means of the first holes 3a and the second holes 3b of which the lower body 3 of the valve group 20 is provided.

[0044] With respect to the intake duct, the first holes 3a are distal, while the second holes 3b are proximal: in other words, these two pluralities of holes are arranged on two different levels along the axial direction of the injector 1.

[0045] The gas outlet is obtained through the plurality of through openings 4a of the cap 4. The number of openings 4a is preferably greater than 1, i.e. these apertures are at least two in number.

[0046] As mentioned, between the needle 5 and the electromagnetic core 7, a gap of axial amplitude p is defined. The value p is the value that the gap assumes when the injector is in the closed position and therefore the value p represents the lift that the needle travels when the power unit 10 is electrically powered. In this situation, the resulting magnetic force that develops, overcoming the elastic reaction of the spring 11, lifts the needle 5 which closes the gap of initial amplitude p. The greater the gap between the needle 5 and the electromagnetic core 7, the greater the magnetic force required to open the injectors and the greater the response time of the injector. According to the present invention and with reference also to Figure 3, two features contribute to increasing the gas flow. Thanks to these two features, even in the presence of a greater gas flow, it is possible to limit the value of the gap and the area, i.e. the external diameter, of the surface 5' of the needle 5 and the corresponding surface 7' of the electromagnetic core 7, facing each other. In other words, it is possible to reduce the magnetic force required for the opening of the injector.

[0047] The two characteristics are: a) a double gas flow path. A primary path 13 starts from the first holes 3a and continues inside the cavity 5a of the needle 5. The gas of the primary path 5 finally reaches the openings 4a of the cap 4, lapping a first radially internal edge 4ai. A secondary path 14 starts from the second holes 3b and continues outside the needle 5, in an annular chamber 3c radially comprised towards the inside by the needle 5 and towards the outside by the lower body 3, finally reaching the openings 4a of the cap 4, lapping a second radially external edge 4ae; b) a radius of curvature or a chamfer on the edges 4ai, 4ae, of the through openings 4a of the cap 4, both in inlet and outlet, to reduce the pressure drops.

[0048] In combination with the double flow path, the position of the plurality of through openings 4a of the cap 4 has been defined to allow a wider flow path, reducing the difference in pneumatic forces as the injection pressure varies between a maximum and a minimum value. By doing so, limiting the lift of the needle to a value lower than 0.5 mm and reducing the pneumatic force, it is possible to use a modular power group derived from known applications, such as the applications of injectors for direct gasoline injection, having a body diameter of less than 25mm.

[0049] According to another aspect of the present invention, a proximal end of the pin 5 has an annular recess 5b shaped to accommodate a sealing element 15 in elastomer with the function of sealing the gaseous fluid between the needle 5 and the cap 4 when the injector 1 is closed. The sealing element 15 and the recess 5b are shaped to reduce wear of the elastomer.

[0050] Furthermore, a pair of guide surfaces 5c of the needle 5 with respect to the lower body 3 is designed to limit the inclination of the needle 5 during operation and consequently to protect the sealing element 15 from wear. Preferably, the pair of guide surfaces 5c of the needle 5 is provided with an antifriction coating to limit wear due to dry running.

[0051] Conveniently, the same antifriction coating covers the facing surfaces 5', 7' of the needle 5 and the electromagnetic core 7 or at least one of them. In this way, a damping characteristic is achieved between the impact surfaces of the armature, i.e. needle 5, and the electromagnetic core 7 during the opening phase of the injector 1.

[0052] Alternatively, as a damping characteristic between the impact surfaces, it is possible to use a softer coating or a layer of rubber instead of the antifriction coating.

[0053] The power group derived from gasoline injectors and the reduced variability of the pneumatic force with the operating pressure allow for a sufficient magnetic force to increase the calibration spring load and consequently the gas tightness with elastomeric material even at lower operating pressures.

[0054] The sealing element 15 in elastomeric material, in addition to seal the injector in the closing phase, dampens the impacts of the needle 5 on the cap 4 in the closing phase, avoiding phenomena of "rebound" of the needle with consequent undesired reopening of the injector.

[0055] With reference to Figures 4 and 5, in a second embodiment of the invention, the sealing element instead of an elastomeric gasket with a conical seal can be made by means of an O-ring 16 housed in a toroidal recess 5d of the proximal end of the needle 5 with the function of sealing between the needle 5 and the cap 4. The gas path remains the same:

[0056] - a primary path 13 that starts from the first holes 3a, continues inside the cavity 5a of the needle 5 and reaches the openings 4a of the cap 4, lapping the first edge 4ai radially inward; and

[0057] - a secondary path 14 that starts from the second holes 3b, continues outside the needle 5 in the annular chamber 3c and finally reaches the openings 4a of the cap 4, lapping the second edge 4ae radially outward.

[0058] With reference to Figures 6 and 7 in a third embodiment of the invention, the cap 40 is provided, instead of through openings in axial direction, with a plurality of radial through holes 40a. The gas path is always double with a primary path 13 that starts from the first holes 3a, continues inside the cavity 5a of the needle 5 and reaches the radial holes 40a of the cap 40 and with a secondary path 14 that starts from the second holes 3b, continues outside the needle \5, in the annular chamber 3c, and finally reaches the radial holes 40a of the cap 40.

[0059] Furthermore, the tightness to the gas flow, in closing conditions of the injector, is ensured by a pair of sealing elements, in the example in Figure 6 a pair of O-rings, interposed between the needle 5 and the cap 40 in which:

[0060] - a first O-ring 17 seals the primary path 13 between the cavity 5a of the needle 5 and the radial holes 40a of the cap 40, and

[0061] - a second O-ring 18 seals the secondary path 14 between the annular chamber 3c and the radial holes 40a of the cap 40.

[0062] In conclusion, the present invention allows to achieve the following advantages:

[0063] - a high static gas flow, for example 5 g / s with a pressure difference of 4.5 bar and a needle lift <500um, thanks to the double path of the gas flow and to the radii of curvature and / or chamfers on the edges of the through openings or on the radial holes of the cap;

[0064] - a reduced difference in pneumatic forces as the supply pressure varies between a maximum and a minimum value, thanks to the optimal position of the plurality of through openings and to the double path of the gas flow;

[0065] - a power group derived from applications for gasoline injection with a body diameter of less than 25mm;

[0066] - a gas seal even at lower operating pressures possible thanks to a higher calibration force of the elastic element.

[0067] 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:- an upper body (2) and a lower body (3), in which the lower body (3) is provided with first (3a) and second through holes (3b) the fuel to enter inside the injector (1),- a cap (4, 40) provided with a plurality of through openings (4a, 40a) for the transit of the fuel from the injector (1) to the intake duct,- a needle (5) configured to unlock and close the openings (4a, 40a) of the cap (4, 40) and to open inwards, and- an electromagnetic actuator (9) for operating the needle (5), the injector (1) being characterized by the fact that it also includes, in combination:- a double fuel flow path, wherein a primary path (13) includes the first through holes (3a), an axial cavity (5a) of the needle (5), in fluid communication with the first holes (3a), and the cap (4, 40) openings (4a, 40a), while a secondary path (14) includes the second through holes (3b), an annular chamber (3c), radially included towards the inside of the needle (5) and towards the outside from the lower body (3), and the cap (4, 40) openings (4a, 40a);- a connecting radius or a chamfer on a first edge (4ai), radially internal, and on a second edge (4ae), radially external, of the cap (4, 40) openings (4a, 40a),- at least a sealing element (15, 16, 17, 18) interposed between theneedle (5) and the cap (4, 40a).

2. Injector (1) according to claim 1, in which a proximal end of the needle (5) has an annular recess (5b) shaped to accommodate an elastomeric sealing element (15) with the function of sealing the fuel between the needle (5) and the cap (4) when closing the injector (1).

3. Injector (1) according to claim 1, in which a proximal end of the needle (5) has a toroidal recess (5d) shaped to accommodate an O-ring (16) with the function of sealing the fuel between the needle (5) and the cap (4) when closing the injector (1).

4. Injector according to claims 2 or 3, wherein the passing through openings (4a) extend in the axial direction.

5. Injector (1) according to claim 1, wherein the cap (40) openings are radial through holes (40a).

6. Injector (1) according to claim 5, in which the seal to the fuel flow, when the injector is closed, is ensured by a pair of O-rings placed between the needle (5) and the cap (40) wherein:- a first O-ring (17) seals the primary path (13) between the cavity (5a) of the needle (5) and the radial holes (40a) of the cap (40), and- a second O-ring (18) seals the secondary path (14) between the annular chamber (3c) and the radial holes (40a) of the bottom (40).

7. Injector (1) according to any of the previous claims, wherein the first through holes (3a) have an internal diameter greater than the internal diameter of the second through holes (3b).

8. Injector (1) according to any of the previous claims, wherein the needle (5) is provided with a pair of guide surfaces (5c) relative to the lower body (3), the guide surfaces (5c) having an anti-friction coating.

9. Injector (1) according to any of the previous claims, in which facing surfaces (5', 7') respectively of the needle (5) and an electromagnetic core (7) of the actuator (9) are provided, both or only one of them, with an anti-friction coating or a layer of rubber.

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

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