EP1599671B1 - Fuel injector for an internal combustion engine - Google Patents

Abstract

A fuel injector comprising a head which has a free outer face and a main orifice designed to spray a fuel jet in a main direction and a secondary orifice designed to spray a fuel jet in a secondary direction, the main and secondary orifices opening into the outer face and communicating directly with a common injection chamber which is selectively placed in communication with a supply chamber. The secondary direction forms an angle alpha between 10° and 80°, with the main direction so that the secondary jet intercepts the main jet in a burst zone which starts at a distance d of between 1 and 15 mm, and the flow rate of the secondary jet is between 80% and 100% of the flow rate of the main jet. The invention also relates to a spark ignition engine and to a method of manufacturing the injector.

Description

The present invention relates to a fuel injector for spraying fuel into the combustion chamber of an engine. More particularly, it relates to an injector comprising a head which has a free outer face and which is provided with at least one main orifice adapted to spray a fuel jet in a so-called main direction and at least one secondary orifice suitable for spraying. a jet of fuel in a so-called secondary direction, said main and secondary openings opening into the outer face and communicating directly with a common injection chamber which is selectively placed in communication with a supply chamber.

For spark-ignition engines with direct fuel injection into the combustion chamber, it is necessary to obtain a well-controlled controlled spray of the fuel jet. Indeed, the spray must have a certain directionality and a penetration speed sufficient to obtain a wealth around the candle at the time of ignition, which ignites the mixture. However, the depth of the spray that increases with the injection pressure must not be excessive, especially in order not to spray fuel against the walls of the combustion chamber.

For this, we used swirl injector injectors in English, in which the fuel is guided in a vortex movement in the injector before being sprayed. These injectors make it possible to obtain a good atomization but, besides their high cost, they have the disadvantage of creating a significant internal pressure drop in the supply pressure and consequently make it essential to apply a high force to operate the needle control of these injectors. In practice, it is difficult to use these injectors with a fuel supply pressure greater than 150 bar. In addition, these injectors create a weakly directional jet with a relatively low rate of penetration into the chamber, which in some cases makes it more difficult to obtain a stratified mixture, i.e. a gas mixture. whose fuel richness is greater in certain parts of the combustion chamber.

For these engines, it is also known to use multi-hole injectors with several orifices that spray fuel jets in divergent directions. These injectors make it possible to obtain a higher penetration speed and a very good directionality of all the fuel jets. In addition, they create less internal pressure losses and are less expensive to manufacture than injectors equipped with a swirling sprayer. On the other hand, the fuel spraying efficiency is lower because the gas contact surface is lower and the fuel jet is less turbulent than the vortex injectors. Consequently, the degree of mixing of the fuel with the gases of the combustion chamber is less controllable in certain cases, which has adverse consequences on the engine performance and the emission of pollutants.

The object of the present invention is to overcome these drawbacks by proposing an injector which allows direct injection under high pressure into the combustion chamber with a high efficiency spray and a certain directionality, without, however, significantly increasing the penetration depth of the combustion chamber. atomized jet of fuel and the cost of the injector.

For this purpose, the invention relates to a fuel injector of the aforementioned type, characterized in that said secondary direction forms an angle α of between 10 ° and 80 °, preferably between 15 ° and 45 °, and even more preferentially approximately equal to 25 °, with said main direction so that the secondary jet intercepts the main jet in a so-called burst zone which starts at a distance d , measured along the main direction from the outer face of the head, included between 1 and 15 mm, and preferably between 1 and 5 mm, and in that the flow rate of the secondary jet is between 80% and 100% of the flow of the main jet.

With this arrangement, from the bursting zone that begins at a short distance from the injector, the main jet is driven by a significant radial velocity component relative to the main direction. From this burst zone, therefore, a better atomization of the main jet and the secondary jet is obtained without, however, completely losing the directional power and the penetration speed of the main jet. In addition, this injector, whose holes can be made by simple cylindrical holes through a metal part, such as a sheet, does not cause significant additional manufacturing cost.

• la face extérieure de la tête comporte au moins une portion présentant une concavité orienté vers l'extérieur, dans laquelle débouche un orifice principal et au moins un orifice secondaire ;
• l'orifice principal et l'orifice secondaire débouchent perpendiculairement à la face extérieure de la tête ;
• la tête est munie d'au moins deux orifices secondaires qui sont régulièrement répartis autour de l'orifice principal ;
• les orifices secondaires présentent des directions secondaires de pulvérisation adaptées pour que les jets secondaires interceptent le jet principal en une même position longitudinale de la direction principale ;
• la tête est munie d'au moins deux orifices principaux adaptés pour pulvériser des jets de carburant selon des directions principales divergentes qui forment entre elle un angle β compris entre 5° et 45° ;
• chaque jet principal est intercepté par au moins deux jets secondaires pulvérisés par des orifices secondaires situés autour de l'orifice principal ;
• l'orifice principal et l'orifice secondaire sont des trous cylindriques, le diamètre de l'orifice secondaire étant inférieur au diamètre de l'orifice principal ;
• la portion concave présente une courbure continue ;
• la portion concave est formée d'au moins deux facettes, une première facette dans laquelle débouche un orifice principal et une facette secondaire dans laquelle débouche un orifice secondaire.

In preferred embodiments of the invention, use is further made of one and / or the other of the following:

• the outer face of the head comprises at least one portion having an outwardly directed concavity into which a main orifice and at least one secondary orifice opens;
• the main orifice and the secondary orifice open perpendicularly to the outer face of the head;
• the head is provided with at least two secondary orifices which are regularly distributed around the main orifice;
• the secondary orifices have secondary spray directions adapted so that the secondary jets intercept the main jet in the same longitudinal position of the main direction;
• the head is provided with at least two main ports adapted to spray fuel jets in divergent main directions which form between it an angle β between 5 ° and 45 °;
• each main jet is intercepted by at least two secondary jets sprayed by secondary orifices located around the main orifice;
• the main orifice and the secondary orifice are cylindrical holes, the diameter of the secondary orifice being smaller than the diameter of the main orifice;
• the concave portion has a continuous curvature;
• the concave portion is formed of at least two facets, a first facet into which opens a main orifice and a secondary facet into which a secondary orifice opens.

Furthermore, the invention also relates to the use of an injector as defined above, with a spark ignition engine, wherein the injector is arranged to directly spray the fuel into the combustion chamber.

• l'injecteur est alimenté en carburant sous une pression présentant une valeur de crête comprise entre 150 et 500 bars ;
• la direction de pulvérisation de l'orifice principal est agencée, en fonction de la géométrie de la chambre de combustion et de la circulation des gaz dans ladite chambre, de manière à obtenir une richesse comprise entre 0,7 et 1,2 à proximité des moyens de commande de l'allumage au moment de l'allumage.

For such use, one or more of the following may be used:

• the injector is supplied with fuel under a pressure having a peak value of between 150 and 500 bar;
• the direction of spray of the main orifice is arranged, depending on the geometry of the combustion chamber and the flow of gases in said chamber, so as to obtain a richness between 0.7 and 1.2 near the control means of the ignition at the moment of ignition.

• la portion concave de la face extérieure est réalisée par déformation d'une portion de paroi initialement plane ; et/ou
• l'orifice principal et l'orifice secondaire débouchant perpendiculairement sont creusés par électroérosion.

The invention also relates to a method of manufacturing an injector as defined above,
in which :

• the concave portion of the outer face is formed by deformation of an initially flat wall portion; and or
• the main orifice and the secondary orifice opening perpendicularly are dug by electroerosion.

• la figure 1 est une vue en coupe simplifiée d'un moteur à allumage commandé et injection directe comprenant un injecteur selon l'invention ;
• la figure 2 est une vue partielle en coupe longitudinale d'un premier mode de réalisation de l'injecteur représenté à la figure 1 ;
• la figure 3 est une vue analogue à la figure 2 sur laquelle est représenté un deuxième mode de réalisation de l'injecteur.

Other features and advantages of the invention will become apparent from the following description, given by way of non-limiting example, with reference to the appended drawings in which:

• Figure 1 is a simplified sectional view of a spark ignition engine and direct injection comprising an injector according to the invention;
• Figure 2 is a partial longitudinal sectional view of a first embodiment of the injector shown in Figure 1;
• Figure 3 is a view similar to Figure 2 which shows a second embodiment of the injector.

In the various figures, the same references have been retained to designate identical or similar elements.

Figure 1 schematically shows a cross section of a four-stroke internal combustion engine, spark ignition and direct fuel injection.

As is well known, the engine 1 comprises one or more cylinders 2 extending along a longitudinal axis XX and in which is slidably mounted according to the longitudinal axis a piston 3. The piston 3 is connected to a crankshaft (not shown) by a connecting rod 4.

A combustion chamber 5 is delimited by the upper end of the cylinder 2, a cavity 6 formed opposite the piston 3 in a cylinder head 7 attached to the cylinder 2, and by an end face 9 of the piston head 8 The cavity 6 of the yoke 7 is a cavity called "roof", that is to say it has two inclined planes connecting at a vertex 6a intersecting the longitudinal axis XX of the cylinder 2.

As regards a spark ignition engine, the cylinder head 7 comprises a spark plug 10 provided with electrodes 11 arranged in the region of the top 6a of the cylinder head. Although particularly intended for this type of engine, it is conceivable that the present invention is applied to a diesel-type compression ignition engine.

The cavity 6 of the cylinder head 7 comprises an intake port 14 at the downstream end of an intake duct 15 and an exhaust port 17 at the upstream end of an exhaust duct 19. The lights intake 14 and exhaust 17 are respectively closed by an intake valve 16 and an exhaust valve 18 whose opening and closing are controlled by any known means, such as a camshaft. Of course, the shape of the combustion chamber 5 and the number of the valves (16, 18) may be different without departing from the scope of the present invention.

The yoke 7 also comprises an injector 12 provided with an injection head 13, which extends along a Y-Y axis. The head 13 of the injector has an outer face 20 arranged in the combustion chamber 5.

The injector 12 is connected to a fuel supply line, not shown. The driving feedstock contains high pressure fuel, that is to say a pressure which reaches at least momentarily a value greater than 100 bar and which substantially corresponds to the pressure at which the fuel is injected into the combustion chamber. In the case of a pipe supplying several injectors under high pressure, this is generally referred to as "common rail". It will be noted, however, that the head of the injector made according to the invention can be used in an injector-pump type injection system in which the injector is associated with a high pressure pump.

As best shown in FIG. 2, the external face 20 of the injector head 13 is provided with a main orifice 21 adapted to spray a jet of fuel, represented schematically by the contour 22, coming from a chamber 24. The jet 22 of the main orifice 21 is oriented in a direction P, said principal, determined by the shape of the orifice 21 and corresponding to the axis of symmetry of the base of the jet 22.

The outer face 20 is also provided with a secondary orifice 25 adapted to spray a jet of fuel 26 in a direction S said secondary. The outer face 20, and more precisely the portion thereof
in which the openings open is free of any obstacle that could hide one or other of the orifices. The secondary orifice 25 also communicates directly with the injection chamber 24 which is thus common to the main and secondary orifices, so that the spraying by the two types of orifice is simultaneous.

To control the fuel injection, the injection chamber 24 is selectively brought into communication with a feed chamber 27 containing pressurized fuel. The communication between the injection chamber 24 and the feed chamber 27 is obtained by raising a needle 28 from a seat 29 formed in the head 13 of the injector. The lifting of the needle 28 can be controlled by mechanical, electromagnetic or piezoelectric means synchronized with the rotation of the crankshaft.

Note that the end 28a of the needle has a complementary geometry to the inner face of the head 13 to minimize the volume of the injection chamber 24, to prevent fuel flow into the combustion chamber 5 to an unwanted moment.

The secondary direction S of the secondary jet 26 is oriented towards the main direction P of the main jet 22 so that the secondary jet 26 intercepts the main jet 22 in a so-called burst zone shown schematically by the contour 30, and the flow the secondary jet 26 is at most equal to the flow of the main jet 22.

With this arrangement, a total or partial collision of the secondary jet 26 with the main jet 22 is obtained, which makes it possible to create, from the burst zone 30, a velocity component in the main jet 22 which is radial relative to the main jet 22. to the main direction P of this jet. This allows a better atomization of the fuel injected into the combustion chamber 5 and consequently to increase the degree of mixing of fuel with the gases contained in the combustion chamber.

Note that to obtain a major burst of the main jet 22, the tests show that the flow of the secondary jet must be at least equal to 80% of the flow of the main jet, so that the amount of movement of the secondary jet reduces by 30% to 40% penetration of the main jet.

In the embodiment shown in FIG. 2, the main direction P and the secondary direction S form between them an angle of about 25 °. However, it is possible to vary this angle according to the ratio between the flow rates of the main jet and the secondary jet, and depending on the degree of bursting of the main jet that is desired. The angle α may be between 10 ° and 80 °, but it is preferable that the angle α remains between 15 ° and 45 °.

The burst zone 30 starts at a distance d measured along the main direction P from the outside face 20 of the injector head 13. This distance d is between 1 and 15 mm to obtain a good compromise between the directionality and the bursting of the main jet 22, but is preferably less than 5 mm to obtain an early burst and a relatively limited penetration depth.

As the flow rate of the jet 22 sprayed through the main orifice 21 is greater than or equal to the flow rate of the secondary jet 26, the directionality and the penetration speed required for the fuel injected into the combustion chamber are obtained, in particular by adjusting the distance between the orifices and the angle α. In addition, the atomized fuel jet forms a solid cone, and not a hollow cone such as that obtained with a vortex injector.

It is not absolutely necessary for the secondary direction S to cut exactly the main direction P. In fact, given the diameters and the flow rates of the main fuel jet and the secondary jet, it is possible to obtain sufficient interception of the fuel jets with a secondary direction S slightly offset from the main direction P, which limits the depth of penetration.

As can be seen in FIG. 2, the main orifice 21 and the secondary orifice 25 are cylindrical holes opening perpendicular to the face outer 20 of the head. These cylindrical holes opening perpendicularly to the outer face 20 are advantageously made by electroerosion. But it is possible to achieve them by other known techniques, such as punching.

However, the orifices (21, 25) could have a different shape, especially in the case of an injector for a diesel engine. Indeed, for this type of engine, the fuel injection pressure is significantly higher, greater than 1000 bar and the wall of the head 13 of the injector is thicker, which allows for the formation of orifices. truncated.

It will be noted that the orifices (21, 25) open directly into the injection chamber 24, which limits the pressure drops in the head of the injector, unlike the vortex injection nozzles which require a device upstream of the orifice to animate the fuel in a circular motion.

The outer face 20 of the head 13 comprises a portion 32 having an outwardly oriented concavity and in which the main orifice 21 and the secondary orifice 25 open perpendicularly, so that the secondary direction S is oriented towards the main direction P.

The concave portion 32 has a continuous curvature that can be obtained by stamping an initially flat sheet metal portion.

As can be seen in Figure 3 which shows a second embodiment of a fuel injector according to the invention, it is possible to multiply the number of main orifices and the number of secondary orifices.

The head 13 of the injector 12 comprises, in this second embodiment, two main orifices (21a, 21b) which respectively spray jets of fuel, not shown, in a main direction Pa and a main direction Pb.

In order to obtain a spray at a wider angle in the combustion chamber, the main directions Pa and Pb are divergent and form between them an angle β of about 15 °. Depending on the characteristics of the fuel spray that are imposed by the geometry of the combustion chamber and the flow of gases, it may be advantageous to vary the angle β between the main directions Pa and Pb of 5 to 45 °.

The outer face 20 of this second embodiment comprises two main orifices (21a, 21b) to which two secondary orifices (25a, 25b) are respectively associated.

The secondary orifices 25a are situated diametrically opposite to the main orifice 21a, which makes it possible to maintain a certain symmetry of the main jet of fuel from the bursting zone. Note that it is possible to maintain this symmetry by having more than two secondary orifices distributed regularly angularly around the main orifice 21a.

The secondary directions Sa jets sprayed by the secondary orifices 25a are arranged so that the secondary jets intercept the main jet of the orifice 21a in a same longitudinal position of the main direction Pa.

The two main orifices (21a, 21b) and the four secondary orifices (25a, 25b) are comprised in the same plane, but it is conceivable to arrange the two main orifices 21a, 21b in a first longitudinal plane of the head 13 of the injector and the secondary orifices (25a, 25b) in two planes perpendicular to the first longitudinal plane.

The outer face 20 comprises a first portion concave 32a in which open the orifices 21a and 25a and a second concave portion 32b into which the openings 21b and 25b. Each concave portion (32a; 32b) has three facets, a central facet into which the main orifice opens perpendicularly and two lateral facets into which the secondary orifices open perpendicularly.

The wall of the injector having the facets is relatively thin in the case where the pressure in the feed chamber 27 does not exceed 500 bars. In order to limit the cost of manufacture, this portion of the outer face having the concavities (32a, 32b) is then formed by stamping, that is to say by deformation and not machining or molding, a portion initially flat.

As shown in Figure 1, the injector made according to the invention is arranged in a spark ignition engine so as to spray the gasoline directly into the combustion chamber. The injector according to the invention makes it possible to very precisely adjust the characteristics of the spray jet, and in particular the direction, speed and depth of penetration, as well as the atomization of the fuel, which is particularly advantageous for this type. engine. Indeed, a spark ignition engine requires a very precise spraying, in particular to have a sufficient wealth in the region of the ignition means at the moment when it is triggered.

The main direction P of the main orifice,
or main orifices, is arranged taking into account the geometry of the combustion chamber, such as the presence of a hollow 33 and a flange 34 formed on the end face 9 of the piston, and the circulation gases inside the combustion chamber to obtain a richness between 0.7 and 1.2 near the electrodes 11 of the spark plug 10 at the time of the creation of a spark between the electrodes.

Note that to obtain a direction of spray of the main orifice arranged correctly, it is possible that the main direction P forms a more or less pronounced angle with the longitudinal axis YY of the injector 12, or that in the case of several main orifices, the main directions (Pa, Pb) are not arranged symmetrically with respect to the longitudinal axis YY of the injector.

The head 13 of the injector made according to the invention creates little internal pressure drop and therefore, the injector 12 can be fed by a common rail containing high pressure fuel. In the case of a spark ignition engine injector, the fuel supply pressure of the injector 12 preferably reaches a peak value of between 150 bar and 500 bar.

Claims (15)

1. A fuel injector for spraying fuel into a combustion chamber (5) of a spark ignition engine, comprising a head (13) which has a free outer face (20) and which is provided with at least one main orifice (21; 21a; 21b) designed to spray a fuel jet in a direction (P; Pa, Pb), called main direction, and at least one secondary orifice (25; 25a, 25b) designed to spray a fuel jet in a direction (S; Sa, Sb), called sencondary direction, said main and secondary orifices opening into the outer face and communicating directly with a common injection chamber (24) internal with said injector, which is selectively placed in communication with a supply chamber (27), characterized in that said secondary direction forms an angle α between 10° and 80°, preferably between 15° and 45°, and more preferably equal to approximately 25°, with said main direction so that the secondary jet (26) intercepts the main jet (22) in a zone (30), called burst zone, which starts at a distance d, measured in the main direction (P; Pa, Pb) from the outer face (20) of the head, of between 1 and 15 mm, preferably between 1 and 5 mm, and in that the flow rate of the secondary jet is between 80% and 100% of the flow rate of the main jet.
2. The injector according to claim 1, wherein the outer face (20) of the head (13) comprises at least one portion (32; 32a, 32b) having an outwardly oriented concavity into which opens a main orifice (21; 21a, 21b) and at least one secondary orifice (25; 25a, 25b).
3. The injector according to claim 2, wherein the main orifice (21; 21a, 21b) and the secondary orifice (25; 25a, 25b) open out perpendicularly to the outer face (20) of the head.
4. The injector according to any one of claims 1 to 3, wherein the head (13) is provided with at least two secondary orifices (25a, 25b) which are uniformly distributed around the main orifice (21a, 21b).
5. The injector according to claim 4, wherein the secondary orifices (25a, 25b) have secondary spray directions (Sa, Sb) designed so that the secondary jets intercept the main jet at the same longitudinal position of the main direction (Pa, Pb).
6. The injector according to any one of claims 1 to 5, wherein the head (13) is provided with at least two main orifices (21a, 21b) designed to spray fuel jets in divergent main directions (Pa, Pb) which between them form an angle β of between 5° and 45°.
7. The injector according to claim 6, wherein each main jet is intercepted by at least two secondary jets sprayed through secondary orifices (25a, 25b) situated around the main orifice (21a, 21b).
8. The injector according to any one of claims 1 to 7, wherein the main orifice (21; 21a, 21b) and the secondary orifice (25; 25a, 25b) are cylindrical holes, the diameter of the secondary orifice being less than the diameter of the main orifice.
9. The fuel injector according to any one of claims 2 to 8, wherein the concave portion (32) has a continuous curvature.
10. The injector according to any one of claims 2 to 8, wherein the concave portion (32a, 32b) is formed by at least two facets, a primary facet into which a main orifice (21a, 21b) opens and a secondary facet into which a secondary orifice (25a, 25b) opens.
11. Use of an injector according to any one of the preceding claims, with a controlled-ignition engine, wherein the injector (12) is arranged so as to spray the fuel directly into the combustion chamber (5).
12. The use of an injector according to claim 11, wherein the injector (12) is supplied with fuel at a pressure having a peak value of between 150 and 500 bar.
13. The use of an injector according to claim 11 or 12, wherein the spray direction (P; Pa, Pb) of the main orifice (21; 21a, 21b) is arranged, as a function of the geometry of the combustion chamber (5) and of the flow of gases in said chamber, so as to obtain a fuel-air ratio of between 0.7 and 1.2 in the vicinity of the ignition control means (11) at the moment of ignition.
14. A method of manufacturing a fuel injector for spraying fuel into a combustion chamber (5) of a spark ignition engine, comprising a head (13) which has a free outer face (20) and which is provided with at least one main orifice (21; 21a; 21b) designed to spray a fuel jet in a direction (P; Pa, Pb), called main direction, and at least one secondary orifice (25; 25a, 25b) designed to spray a fuel jet in a direction (S; Sa, Sb), called sencondary direction, said main and secondary orifices opening into the outer face and communicating directly with a common injection chamber (24) internal with said injector, which is selectively placed in communication with a supply chamber (27), characterized in that a concave portion (32; 32a; 32b) of the outer face (20) of the head (13) is produced by deformation of an initially flat wall portion, and in that the main orifice (21;21a,21b) and the secondary orifice (25;25a,25b) are cut throught the head (13) such that said secondary direction forms an angle α between 10° and 80°, preferably between 15° and 45°, and more preferably equal to approximately 25°, with said main direction so that the secondary jet (26) intercepts the main jet (22) in a zone (30), called burst zone, which starts at a distance d, measured in the main direction (P; Pa, Pb) from the outer face (20) of the head, of between 1 and 15 mm, preferably between 1 and 5 mm, and in that the flow rate of the secondary jet is between 80% and 100% of the flow rate of the main jet.
15. A method of manufacturing an injector according to claims 14, wherein the main orifice (21; 21a; 21b) and the secondary orifice (25; 25a; 25b) are cut by electrical discharge machining so that they open out perpendicularly to the outer surface (20).

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