FR2866393A1 - Internal combustion engine, has piston with cavity for cooperating with two sheets when piston reaches top dead center, where cavity is shaped such that sheets do not interfere with each other, when fuel is simultaneously injected in sheets - Google Patents

Abstract

The engine has housing with a cylindrical bore (3), a cylinder head (4), a piston (5) provided in a cylinder (2) and a fuel injector (18) controlled by a control unit for injecting fuel into two separate sheets. The piston has a cavity for cooperating with the sheets when the piston reaches top dead center. The cavity is shaped such that the sheets do not interfere with each other, when fuel is simultaneously injected in the sheets.

Description

2866393 1

  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 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 comprises a central portion or raised nipple 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 can 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 pressure greater than 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 fuel jets ; - 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.

  2866393 4 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 bring 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 cylinder, a fuel injector controlled by electronic control means.

  According to the invention, the 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 said plies during the passage the piston in the vicinity of top dead center, the cavity being shaped so that the two plies do not interfere directly when the fuel injection is operated simultaneously according to the first and second plies.

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

  According to another characteristic of the engine that is the subject of the invention, the top of said first fuel ply extends at a distance from the gasket plane of the cylinder head substantially less than the distance separating the top of the second fuel ply from the fuel plane. cylinder head gasket.

  According to another characteristic of the engine which is the subject of the invention, the first ply has an apex angle (beta1) of between 140 and 175.

  According to another characteristic of the engine which is the subject of the invention, the second ply has an apex angle (beta 2) of between 90 and 160.

  According to another characteristic of the engine which is the subject of the invention, the cavity formed in the piston head comprises an annular groove delimited towards the opening of the cavity by a step and a central protuberance facing the injector.

  According to another characteristic of the engine object of the invention, the redan extending in the cavity formed in the piston head is arranged to be impacted by said first web.

  According to another characteristic of the engine which is the subject of the invention, the central protuberance extending into the cavity formed in the piston head is of substantially conical shape and is arranged so that it can be swept by the second fuel ply.

  According to another characteristic of the engine which is the subject of the invention, the cavity formed in the piston head satisfies the relationship: 2.8 <Dbol / Hbol <3.6; with 2866393 6 Dbol: maximum diameter of the annular groove; Hbol: maximum depth of the cavity.

  According to another characteristic of the engine according to the invention, the cavity 5 formed in the piston head satisfies the relationship: 5% <((Dbol Dcol) / Dbol * 100) <9%, with Dbol: maximum diameter of the throat annular; Dcol: minimum diameter at the level of the redan.

  The present invention and its advantages will be better understood on studying the detailed description of an embodiment given by way of nonlimiting example and illustrated by the appended drawings, in which: FIG. 1 represents a sectional view schematic and partial 15 of an internal combustion engine; - Figures 2, 3a and 3b show schematic sectional views of a bi-nappe injector; FIG. 4 is a partial view in axial section showing the shape of a piston according to the invention; Figure 5 is a detailed view of the piston shown in Figure 4 specifying the impact zones of the fuel jets, when the piston 25 is in the vicinity of the top dead center.

  In Figure 1, a motor housing 1 comprises a cylinder 2 provided with a bore 3 and closed at its upper end by a cylinder head 4. A piston 5 slides in the bore 3 of the cylinder 2, forming between the upper surface 6 of the piston, the top of the bore 3 and the lower surface facing the cylinder head 4 a combustion chamber 7.

  The cylinder head 4 comprises inlet gas intake means formed by at least one duct 8 opening into the roof of the chamber 7 through an opening 9, and a control valve 10 able to be actuated between a closed position. shutter opening 9 and an open position of gas admission. 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 improving the guiding of 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 engine crankshaft, 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 bi-layer type injection head 19 has a first series of holes 191 intended to produce a first conical nimble sheet of fuel N1, having a beta angle at the top. This sheet N1 is formed, for example, by at least four holes and therefore four jets of fuel.

  The twin-ply injection head 19 has a second set of holes 192 formed under the holes of the first ply towards the plunger. 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 a beta 1 angle between 140 and 175, and the point of competition of its jets is located at a distance D21 from the joint plane of the yoke 4. The second ply N2 has a beta2 angle of between 90 and 150 degrees, and the point of competition of its jets is located at a distance D22 of the joint plane of the cylinder head 4. The distances D21 and D22 are dependent on the geometry of the injector and its implantation in the cylinder head.

  There are different possibilities to arrange the holes 191 of the first ply N1 and the holes 192 of the second ply N2, with respect to one another. A first realization, cf. Figure 3a is to arrange the holes so that the jets are superimposed. In a second embodiment, cf. Figure 3b, the holes are arranged in staggered rows.

  The injector 18 is shaped to selectively drive 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 operating point 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 FIG. 4, the upper surface 6 of the piston 5 comprises a central cavity 22. In the illustrated example, this cavity 26 is surrounded by a substantially flat circular hunting zone 23 facing the lower surface of the 4. This presented hunting zone extending perpendicular to the axis of the piston could obviously not be. In the embodiment of FIG. 4, taken as a 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 side wall defining first groove 25, a second annular groove 26 and between them, a convex connection zone 27, also called redan (or reentrant) and a bottom wall having a projecting central protuberance 28.

  This central protuberance 28 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 yoke 4 when the piston 5 is at TDC. This conical central protrusion 28 is adapted to have an apex angle substantially close to beta 2 and a positioning adapted so that the second ply N 2 comes to scan it and is thus directed towards the bottom of the groove 26. The step 27 is positioned to receive the first sheet N 1.

  The maximum diameter of the cavity 26 is defined by the magnitude Dbol to the right of the second annular groove 26, and the minimum diameter at the redan 27 is Dcol. Finally, Hbol represents the maximum depth of the cavity 22 with respect to the opening 24.

  Referring to Figure 5, 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 N 1 and N 2, 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 for the sheet N 2 to fill the annular groove 26 where the air / fuel mixture takes place and does not interfere directly with the sheet N 1. It is also important that the sheet N1 is well distributed both to the hunting area and to the center of the combustion chamber. This distribution is ensured by the rounded redan 27 which receives the sheet N1 and limits the penetration of the sheet N1 in the direction of the annular cavity 26.

  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 Dbol and its depth Hbol is well proportioned, that is to say that the ratio Dbol / Hbol is between 2, 8 and 3.6. Thus, there is a space to obtain the desired wealth while allowing the two layers of jets N1 and N2 fuel not to be in interference with each other.

  On the other hand, in order to promote the ejection of the gases located in the cavity 22 towards the hunting zone 23 during the expansion, that is to say during the descent of the piston 5, the percentage of redan defined by the ratio (Dbol - Dcol) / Dbol * 100 must be between 5% and 9%.

  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. The opening angles of this ply proposed by the Applicant allow to inject the fuel according to a so-called conventional concept where a single-ply injector is mounted.

  Of course, the invention is not limited to the embodiments that have been specifically described in the current examples above and that it extends on the contrary to any variant using equivalent means.

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 cylinder, a fuel injector (18) controlled by electronic control means , 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 (26) intended to cooperate with said plies during the passage of the piston (5) in the vicinity of the top dead center, said cavity (26) being shaped so that the two plies do not interfere directly when the fuel injection is operated simultaneously according to said first and said second plies ( N1, N2).   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.   5. Internal combustion engine according to claim 2, characterized in that said second ply (N2) has an apex angle (beta2) of between 90 and 160.   6. Internal combustion engine according to any one of the preceding claims, characterized in that said cavity comprises an annular groove (26) defined towards the opening (24) of the cavity (23) by a redan (27) and a central protuberance (28) facing the injector (18).   7. Internal combustion engine according to claim 6, characterized in that said step (27) is arranged to be impacted by said first web (NI).   8. Internal combustion engine according to any one of claims 6 or 7, characterized in that said central protuberance (28) is of substantially conical shape and in that said central protuberance (28) is arranged so as to be able to be swept by said second web (N2).   9. Internal combustion engine according to claim 6, characterized in that the cavity (22) satisfies the relationship: 2.8 <Dbol / Hbol <3.6; with Dbol: maximum diameter of the annular groove (26); Hbol: maximum depth of the cavity (22).   10. Internal combustion engine according to claim 6, characterized in that the cavity (22) satisfies the relationship: 5% <(Dbol-Dcol) / Dbol * 100) <9%, with Dbol: maximum diameter of the annular groove (26); Dcol: minimum diameter at the redan (27).