FR2868480A1 - Internal combustion engine e.g. direct injection engine, has piston with central cavity formed by upper and lower annular grooves that are separated by transom, where grooves are arranged for receiving respective fuel slicks - Google Patents

Abstract

The engine has a fuel injector controlled by an engine control system for proceeding fuel injection based on distinct fuel slicks (N1, N2). A piston has a central cavity (22) that cooperates with the slicks during passage of the piston near top dead center. The cavity is formed by upper and lower annular grooves (25, 26) that are separated by a transom (R2). The grooves are arranged for receiving respective slicks.

Description

INTERNAL COMBUSTION ENGINE WITH DIRECT INJECTION

  The invention relates to an internal combustion engine and more particularly to a direct injection engine. The present invention more particularly relates to compression ignition type engines operating according to the Diesel cycle.

  The present invention also relates to a piston for an internal combustion engine for producing such an engine.

  US Pat. No. 5,150,677 or US Pat. No. 5,868,112 discloses a direct fuel injection engine comprising a casing in which several cylinders are arranged, pistons sliding in the cylinders and a cylinder head closing the upper end. crankcase.

  The cylinder head comprises for each cylinder: intake and exhaust ducts selectively closed by at least one (preferably two) intake valve mounted in the cylinder head, at least (preferably two) an exhaust valve mounted in the breech.

  A fuel injector is also housed in the cylinder head facing each cylinder, this injector opening into the lower part of the cylinder head facing the cylinder, approximately in the center of it.

  The pistons are shaped to have on their upper face facing the cylinder head, a central cavity shaped bowl 30 surrounded by an annular hunting area.

  For each cylinder, the combustion chamber of this type of engine is thus formed by the surface of the cylinder head facing the cylinder, the cylindrical upper wall of the housing facing the cylinder head and the upper surface of the piston.

  The shape of this combustion chamber depends on the quality of the preparation of the fuel mixture and hence the quality of the combustion. This form is therefore carefully studied especially vis-à-vis the jet of fuel injected and the positioning of the intake and exhaust valves.

  Many forms of profile of the bowl formed in the piston head have been proposed both for the purpose of improving the performance of the piston as in that of limiting fume emissions related to poor removal of soot.

  In general, the diesel injection chambers with direct injection under high pressure or common rail currently used, have the following features: - The piston bowl is axisymmetric and vertical axis: it has a central part or raised nipple is connecting to a side or exterior wall which may be vertical or have a concavity. The central portion may be alpha corner cone shaped, as shown in the patents mentioned above; exceptionally, the lateral part may be flared, as shown in patents US4662319, US4161165 or US4242948, but the preference generally goes to a concave shape - the injector sends several jets (at least four) of fuel under high pressure (a higher pressure at 600 bars) arranged on a cone of beta angle, called the lap angle, and axis coinciding with the axis of the bowl, this fuel injection device in the combustion chamber traditionally has a single layer of jet of fuel; - The main injection is near the top dead center (TDC), that is to say close to the plane of the cylinder head; the fuel shafts intersect the outer wall of the bowl when the piston is at the top dead center, as can be seen for example in the figures of document US Pat. No. 4,635,597, and the result is a vortex movement of horizontal axis intended to deflect the mixture of first down then the center of the bowl.

  It was generally believed that this prior art was generally satisfactory. However, further studies of the course of the combustion have allowed the Applicant to note an incomplete use of the volume of the cavity by the high-speed combustion: oxygen remains unused, which degrades combustion and polluting emissions or even degrades performance for the same level of pollutant emissions. Moreover, even at low speed, there is a risk of confinement of combustion in the cavity and misuse of the cylinder area when the piston goes down.

  It is possible to improve the distribution of fuel in the combustion chamber by using an injector having the particularity of allowing the creation of two plies of fuel jets (at least four per ply), called bi-layer injector.

  Reference can be made to references WO0242631, DE10058153, for a description of these injectors. This type of injector makes it possible to inject the fuel into the combustion chamber selectively or cumulatively in a first so-called open-angle ply web and a second so-called narrow-angle ply web.

  The bi-layer injector allows operation with a single sheet (preferably the sheet 1) mainly in partial load (or engine operating point lightly loaded) and thus allows the use of a low permeability to provide a gain in terms of pollutant emissions. In a second type of operation, mainly at high speed and high load, the two sheets of the injector are open and can improve the performance of the engine.

  The proposed invention thus consists in proposing, in the context of an engine equipped with a bi-layer injector, an optimized shape of the cavity formed in the piston adapted both to an operation of the injector with the two open webs. (Highly loaded operating point) and single-layer low-load operation.

  The object of the invention is to improve the operation and performance of an engine by optimally using the volume of the cavity at all speeds. The invention more precisely to optimize the shape of the cavity to allow optimum distribution of fuel from a bi-nappe injector.

  The internal combustion engine according to the invention comprises a housing having a cylindrical bore, a cylinder head, a piston housed in the bore, a fuel injector controlled by electronic control means.

  According to the invention this engine is characterized in that the injector is adapted to inject the fuel in a first and / or a second separate ply and in that the plunger comprises a cavity intended to cooperate with these plies during the passage of the piston. in the vicinity of the top dead center, the cavity being shaped so as to have a lower annular groove and an upper annular groove, these grooves being separated by a step, the lower groove being arranged to receive the second layer and said upper groove being arranged to receive the first tablecloth.

  According to another characteristic of the engine that is the subject of the invention, the first and second plies are substantially conical and substantially coaxial, the first ply enveloping the second ply.

  According to another characteristic of the engine which is the subject of the invention, the top of the first ply extends at a distance from the joint plane of the yoke substantially less than the distance separating the top of said second ply to said joint plane of the bolt .

  According to another characteristic of the engine which is the subject of the invention, the first ply has an apex angle of between 140 and 175 and in that said second ply has an apex angle of between 90 and 160.

  According to another characteristic of the engine according to the invention, the cavity formed in the piston comprises a bottom wall having a central protuberance facing the injector.

  According to another characteristic of the engine which is the subject of the invention, the central protuberance is of substantially conical shape and the central protuberance is arranged so that it can be swept by the second ply.

  According to another characteristic of the engine which is the subject of the invention, the cavity formed in the piston comprises a second step extending in the vicinity of the opening of the cavity, the second redan being arranged so as to be able to be impacted by the first layer. .

  According to another characteristic of the engine object of the invention, the upper groove is extended towards the opening of the cavity by a flared wall intended to be impacted by the first ply.

  According to another characteristic of the engine which is the subject of the invention, the cavity formed in the piston satisfies the relationship: 0.4 <H / Hbol <0.8; with Hbol: maximum depth of the cavity (22) and, H: depth of the first step (R2).

  According to another characteristic of the engine which is the subject of the invention, the cavity formed in the piston satisfies the relationship: 5% <(max (Dbol1, Dbol2) Dcol2) / max (Dboll, Dbol2) <9%, with Dbol 1: diameter maximum of the lower annular groove (26); Dbol2: maximum diameter of the upper annular groove (25); Dcol2: minimum diameter at the first step (R2) The present invention and its advantages will be better understood from the study of the detailed description of an embodiment given by way of non-limiting example and illustrated by the accompanying drawings, in which: - Figure 1 shows a schematic and partial sectional view of an internal combustion engine; FIGS. 2, 3a and 3b show a diagrammatic and partial sectional view of a bi-nappe injector; - Figures 4a and 4b show a partial view in axial section specifying two embodiments of the form of a piston according to the invention; - Figures 5a and 5b show detailed views of the two embodiments of the piston shown respectively in Figures 4a and 4b specifying the impact zones of the fuel jets, when the piston is in the vicinity of the top dead center.

  In Figure 1, the housing of the engine 1 according to the invention comprises a cylinder 2 provided with a bore 3. The cylinder 2 is closed at its upper end by a yoke 4 overlying said housing. A piston 5 is slidably mounted in the bore 3 of the cylinder 2. Between the upper surface 6 of the piston 5, the top of the bore 3 and the lower surface opposite the cylinder head 4, there is a combustion chamber 7. .

  The yoke 4 comprises admission gas intake means formed by at least one duct 8 opening into the roof of the chamber 7 through an opening 9 cooperating with a control valve 10 adapted to be actuated between a closed position of closing the opening 9 and an open position of admission of the gases. The valve 10 comprises a control rod 11 and a frustoconical shutter head 12 whose inclined peripheral surface comes into contact with a corresponding surface of the valve seat opening 9 to close the opening 9.

  The yoke 4 comprises means for exhausting the flue gases formed by at least one exhaust duct 13 opening into the roof of the chamber 7 through an opening 14 adapted to be closed by a control valve 15 comprising an actuating rod 16 and a sealing head 17.

  The yoke 4 also comprises a fuel injection means formed by a controlled injector 18 receiving at an external inlet the fuel under a suitable pressure and having at one end projecting into the chamber 7 an injection head 19 adapted to spray the fuel. fuel in the form of fine droplets in the chamber 7 at the appropriate time determined by the engine control system not shown, which in particular pilot the injection time and the duration of injection (that is to say, the amount injected) .

  The piston 5 comprises a head 20 whose upper surface 6 facing the yoke forms the bottom wall of the chamber 7, and a skirt 21 for guiding the piston in translation in the cylinder 2. The piston 5 also comprises a tab of fixing comprising an axis on which is fixed the head of a connecting rod for converting the translational movement of the piston 5 into rotational movement of a crankshaft, not shown in Figure 1.

  During the rotation of the crankshaft of the engine, the piston 5 moves between a position of bottom dead center, or PMB, remote from the cylinder head 4, and a position of top dead center, or TDC, close to the cylinder head 4.

  Referring to FIGS. 2, 3a and 3b, the injection head 19 of the central fuel injector 18 has been detailed.

  This injection head 19 of bi-sheet type has a first series of holes 191 for producing a first conical N1 fuel fillet, beta angle apa1. This sheet N1 is formed, for example, by at least four holes and therefore four jets of fuel.

  The injection head 19 of bi-sheet type has a second series of holes 192, formed under the holes of the first sheet in the direction of the piston. This second series of holes being intended to produce a second conical layer of fuel N2, with an angle at the top beta2. This sheet N2 is formed, for example, by at least four holes and therefore four jets of fuel.

  The first ply N1 has an angle at the apex beta 1 between 140 and 175, and the point of concurrence of its jets is located at a distance D21 from the joint plane of the yoke 4. The second ply N2 has a vertex angle beta2 between 90 and 150 degrees, and the point of competition of its jets is located at a distance D22 from the joint plane of the cylinder head 4. The distances D21 and D22 are dependent on the geometry of the injector and its location in the However, cylinder head D21 remains substantially less than distance D22.

  There are different possibilities to arrange the holes 191 of the first ply N1 and the holes 192 of the second ply N2, relative to each other. A first embodiment shown in Figure 3a is to arrange the holes so that the jets are superimposed. In a second embodiment shown in Figure 3b, the holes are arranged in staggered rows.

  The injector 18 is shaped to be selectively controlled by the engine control system to operate the fuel injection according to one and / or other of the plies N1, N2 and according to the point of operation of the engine. Thus at high load, the fuel is injected simultaneously via the two sheets N1 and N2, while in partial load, the fuel is injected in the form of the single sheet N1.

  Referring to FIGS. 4a and 4b, the upper surface 6 of the piston 5 comprises a central cavity 22. In the illustrated examples, this cavity 22 is surrounded by a substantially flat circular hunting zone 23 facing the corresponding lower surface. the cylinder head 4. This hunting zone presented extending perpendicular to the axis of the piston could obviously not be.

  In the embodiment of Figure 4a, taken by way of non-limiting example, the central cavity 22 is symmetrical in revolution along the main axis of the piston 5. This cavity 22 is formed from its opening of a wall curved redan R1, an annular groove also called upper groove, then another annular groove 26 also called lower groove, the two annular grooves being separated by a second curved wall R2 in redan, and finally a wall of protruding bottom having a central protuberance 28.

  In the embodiment of Figure 4b, taken by way of non-limiting example, the central cavity 22 is symmetrical in revolution along the main axis of the piston 5, and comprises an opening 24, a flared side wall E, two grooves annular 25 and 26, separated by a bulging wall R2 in redan and a bottom wall having a projecting central protuberance 28.

  The central protrusion 28 common to both embodiments is, for example, conically shaped and its rounded top is shaped to be at a distance D 1 (generally between 4mm and 6mm) of the joint plane of the cylinder head 4 when the piston 5 is at the PMH. This conical central protrusion 28 is adapted to have an apex angle substantially close to beta 2, the apex angle of the second ply N 2, and a positioning adapted for the second ply N 2 to come and sweep it and thus be directed towards the bottom of the throat 26.

  In the first embodiment, the redan R1 is positioned to receive the first web N1 while the second embodiment, described in Figure 4b, is the flared wall E which receives the web N1.

  In the first embodiment shown in FIGS. 4a and 5a, the maximum diameters of the cavity 22 are respectively defined by the sizes Dbol1 at the right of the upper annular groove 25, and Dbo12 at the right of the lower annular groove 26, the diameters The minimum values are respectively defined by the variables Dcol 1 at the level of the redan R1 and Dco12 at the level of the redan R2. Hbol represents the maximum depth of the cavity 22 with respect to the opening 24. Finally, H represents the depth of the step R2 relative to the opening 24.

  In the second embodiment shown in Figures 4b and 5b, the maximum diameter of the cavity 22 at the lower annular groove 26 is defined by the size Dbol2, the minimum diameter of the cavity 22 is defined by the size Dcol2 at level of the redan R2, the maximum diameter of the cavity 22 to the right of the upper annular groove 25 is defined by the size Dbol l, and theta represents the angle made by the flared wall E with the vertical. Hbol represents the maximum depth of the cavity 22 with respect to the opening 24. Finally, H represents the depth of the step R2 relative to the opening 24.

  Referring to Figures 4a and 4b, we see the interaction of the two fuel plies N1 and N2 and the cavity 22. This situation corresponds to a high load operation where the amount of fuel injected is the largest and where the fuel is injected through the two layers N1 and N2, in superimposed configuration.

  In order to promote the preparation of the air / fuel mixture necessary for the smooth running of the combustion, it is important that the sheet N2 fills the lower annular groove 26 where the air / fuel mixture takes place and does not interfere directly with the sheet N1. . It is also important that the sheet N1 is well distributed both to the hunting zone and to the center of the combustion chamber 7.

  In the embodiment shown in FIG. 4a, this distribution is ensured by the upper rounded step R1 which receives the sheet N1 and limits the penetration of the sheet N1 towards the upper annular cavity 25.

  In the embodiment shown in Figure 4b, this distribution is provided by the flared wall E which is particularly justified when the piston back down, thereby promoting the evacuation of fuel to the hunting areas.

  In order to optimize this distribution of fuel in a bilayer operation, it is necessary to ensure that the ratio between the diameter of the bowl Dbo12 to the right of the lower annular groove 26 and its depth Hbol is well proportioned, that is, the Dbol2 / Hbol ratio is between 2.8 and 3.6.

  Thus, there is a geometry to obtain a sufficiently deep space to spare the redan R2. On the other hand, it is necessary to ensure that the ratio between the diameters Dboll and Dbol2 to the right of the annular grooves 25 and lower 26 is well proportioned, that is to say that the ratio Dbol1 / Dbo12 is included between 0.8 and 1.2. These two constraints make it possible to obtain the desired wealth while allowing the two layers of jets N1 and N2 of fuel not to be in interference with each other In order to promote the guiding of fuel in the cavity 22 as shown in Figures 5a and 5b, the redan R2 should not be too prominent and meet the geometric constraint defined by the relationship ((max (Dboll, Dbol2) - Dcol2) / max (Dboll, Dbol2)) <9%. On the other hand, the presence of the redan R2 is effective only by respecting the geometric constraint defined by the relation 5% <((max (Dbol1, Dbol2) - Dcol2) / max (Dboll, Dbol2)).

  In order to correctly position the redan R2 in the cavity, and to provide the space required for the two upper and lower annular grooves 26 respectively receiving the two sheets N1 and N2, it is important that the H / Hbol ratio be between 0.4 and 0.8. .

  In the embodiment described in FIGS. 4a and 5a, the upper step R1 is intended to receive the jet of fuel coming from the sheet N1. Its function is to distribute well on the one hand to the upper groove 25 and on the other hand to the hunting zone 23 the fuel.

  This redan R1 should not be too prominent and respect the geometrical constraint defined by the relation ((max (Dbol1, Dbol2) - Dcoll) / max (Dboll, Dbol2)) <9%. On the other hand, the presence of the upper redan R1 is effective only by respecting the geometric constraint defined by the relation 5% <((max (Dboll, Dbol2) - Dcoll) / max (Dbol1, Dbol2)) . This geometrical constraint is, moreover, motivated by the fact of favoring the ejection of the gases situated in the cavity 22 towards the hunting zone 23 during the expansion, that is to say during the descent of the piston 5.

  In the embodiment described in FIGS. 4b and 5b, the flared wall E is intended to receive the jet of fuel coming from the sheet N1. Its function is to guide the fuel towards the hunting zones 23 when the piston goes down. This flared wall forms a theta angle with the vertical preferably between 0 and 5.

  This configuration of the cavity 22 is also well suited to an operating mode where only the web N1 is present. This configuration is generally used for part-load engine operation.

  In-depth studies of the combustion process for a conventional diesel combustion system have shown an incomplete use of the volume of the cavity 22 by the combustion at high speed: oxygen remains unused, which degrades the combustion and the combustion processes. emissions or degrades performance for the same level of pollutant emissions.

  The proposed invention improves the distribution of fuel in the combustion chamber using an injector having the particularity of allowing the creation of two layers of fuel jets combined with an optimized form of the cavity 22 formed in the piston, the cavity 22 being shaped to have a lower annular groove 26 for receiving the web N2 and an upper annular groove 25 for receiving the web N1, these grooves being separated by a redan R2.

  To ensure the smooth running of the combustion, it is necessary to concentrate on creating a good preparation of the air / fuel mixture by optimizing the use of the available oxygen in the combustion chamber while limiting the zones. over-riches responsible for the formation of particles. On the one hand, the invention proposes to limit as much as possible the interaction of the two fuel jets N1 and N2 by placing a redan R2 acting as a deflector of the aerodynamic flow in the cavity 22. D On the other hand, the sheet N2 cooperates with the central pin 28 in order to confine the fuel just needed to consume the oxygen available in the cavity 26. In a symmetrical manner, the sheet N1 is intended to cooperate with the cavity 25 to consume the fuel. oxygen remaining available in the cavity 22.

Claims (10)

CLAIM   An internal combustion engine comprising a housing (1) having a cylindrical bore (3), a cylinder head (4), a piston (5) housed in said bore (3), a fuel injector (18) controlled by means control electronics, characterized in that said injector (18) is adapted to inject the fuel in a first and / or a second separate ply (N1, N2) and in that said plunger comprises a cavity (22) intended to cooperate with said plies during the passage of the piston (5) in the vicinity of the top dead center, said cavity (22) being shaped to present a lower annular groove (26) and an upper annular groove (25), said grooves being separated by a redan (R2), said lower groove (26) being arranged to receive said second ply (N2) and said upper groove being arranged to receive said first ply (Ni).   2. Internal combustion engine according to claim 1, characterized in that said first and second plies (N1, N2) are substantially conical and substantially coaxial, said first ply (Ni) enveloping said second ply (N2).   3. Internal combustion engine according to claim 2, characterized in that the top of said first ply (N 1) extends at a distance (D21) from the joint plane of the yoke (4) substantially less than the distance ( D22) separating the top of said second ply (N2) from said joint plane of the yoke (4).   4. Internal combustion engine according to claim 2, characterized in that said first ply (Ni) has an apex angle (beta1) of between 140 and 175 and that said second ply (N2) has an apex angle ( beta2) between 90 and 160.   5. Internal combustion engine according to any one of the preceding claims, characterized in that said cavity (22) comprises a bottom wall having a central protuberance (28) facing the injector (18).   6. Internal combustion engine according to claim 5, characterized in that said central protuberance (28) is of substantially conical shape and in that said central protuberance (28) is arranged so that it can be swept by said second ply ( N2).   7. Internal combustion engine according to any one of the preceding claims, characterized in that said cavity (22) comprises a second step (R1) extending in the vicinity of the opening (24) of said cavity (22), said second redan (R1) is arranged to be impacted by said first web (N 1).   8. Internal combustion engine according to any one of the preceding claims, characterized in that said upper groove (25) is extended towards the opening (24) of said cavity by a flared wall (E) intended to be impacted. by said first web (Ni).   9. Internal combustion engine according to claim 6, characterized in that the cavity (22) satisfies the relation: 0.4 <H / Hbol <0.8; with Hbol: maximum depth of the cavity (22) and, H: depth of the first step (R2).   10. Internal combustion engine according to claim 6, characterized in that the cavity (22) satisfies the relationship: 5% <(max (Dbol 1, Dbol 2) Dcol 2) / max (Dbol 1, Dbol 2) <9%, with Dbol 1: maximum diameter of the lower annular groove (26); Dbo12: maximum diameter of the upper annular groove (25); Dco12: minimum diameter at the first step (R2).