FR2834002A1 - Internal combustion engine with compression ignition has combustion chamber defined on one side by top of piston and on other by lower wall of cylinder head having recess with fuel injection nozzle and spark plug opening into same - Google Patents

Abstract

The combustion chamber (1) is defined on one side by the top of a piston (3) mounted in a cylinder block and on the other side by the lower wall of a roof-shaped cylinder head (4). The cylinder head has a recess (18) opening into the lower wall of same and the fuel injection nozzle (16) is mounted parallel to axis of the cylinder to open in the upper part of the recess. A spark plug (17) opens at the side in the recess and the piston has on its top side an indentation (30) set underneath the recess and enclosed by two protruding shoulders (33) set symmetrical relative to the transverse plane of the cylinder.

Description

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Compression ignition internal combustion engine
The present invention relates to an internal combustion engine with compression ignition, for example diesel, with direct fuel injection intended in particular to equip a motor or road vehicle.

The present invention relates more particularly to the shape of the combustion chamber of an engine and in particular the upper face of the piston.

 French patent application NOOl-12306 (machining of a conical chamber) describes a multi-cylinder diesel engine type and direct injection, in the fuel injectors are arranged substantially in the axis of the cylinders, the conical chamber being formed in the breech.

 This central position of the fuel injector in a roof or conical cylinder head has the advantage of limiting the phenomena of wall wetting (in the case where the fuel is injected either very early in the cycle, in the compression phase or very late in the expansion phase), that is to say the deposition of fuel particles on the walls of the cylinder, and therefore limit the significant emissions of polluting substances such as HC and simultaneously Nox and particles.

 According to the aforementioned document, it is also known to open a glow plug (opening either laterally in the recess as close as possible to the injector or directly in the cylinder between 2 valves).

 The shapes of the known pistons, flat having a cavity (of the type of a closed lip cup), associated with a flat cylinder head have the drawback of not satisfying optimally the two main operating modes encountered by direct injection engines. diesel, namely stratified and homogeneous operations. Indeed, so far, when the piston geometer is adapted to the preparation of the stratified charge and the local concentration of the

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 combustion then it is the operation under homogeneous load which is degraded and vice versa, when the geometry of the pistons and of the cylinder head is adapted to the operation under homogeneous load then it is the operation in laminate mode which is penalized.

 The object of the present invention is therefore to produce a diesel internal combustion engine and direct fuel injection of a new design which overcomes the aforementioned drawbacks, in particular by means of a piston of suitable shape associated with a roof or conical cylinder head allowing both stratified and homogeneous operations.

 This object is achieved by a diesel internal combustion engine comprising a combustion chamber delimited on the one hand by the upper wall of a piston mounted in a cylinder block and on the other hand by the lower wall of a cylinder head on the roof. comprising, on one side of the roof surface, two separate inlet openings and on the side opposite to the inlet openings, by two separate exhaust openings, and characterized in that the cylinder head further comprises a recess opening into the lower wall of the cylinder head, a fuel injector arranged parallel to the axis of the cylinder and opening at the top of the recess, a preheating plug opening laterally in the recess and in that the piston is provided on its wall upper of a cavity extending substantially under said recess, said cavity being surrounded by two projecting bosses which extend symmetrically with respect to the transverse plane of the cylinder.

 According to another characteristic of the diesel internal combustion engine object of the invention, the recess is formed by a main cavity delimited by a bottom which opens out towards the nose of the injector and a side wall, and a plurality of secondary cavities opening out. in the lower part of the main cavity.

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 According to another characteristic of a diesel internal combustion engine object of the invention, said main cavity extends substantially in the axis of the cylinder.

 According to another characteristic of the internal combustion engine object of the invention, the main cavity is of substantially circular or elliptical section.

 According to another characteristic of the diesel internal combustion engine object of the invention, the secondary cavities extend on either side of the main cavity between the intake and / or exhaust ports.

 According to another characteristic of the diesel internal combustion engine object of the invention, the bosses formed on the upper face of the piston around on either side of the cavity extend according to an angular sector between 900 and 1300.

 According to another characteristic of the internal combustion engine object of the invention, the bosses formed on the upper face of the piston on either side of the cavity have ends extending under the intake and exhaust ports which are Conformed to generate consequent hunting zones oriented towards the center of the cavity.

 According to another characteristic of the diesel internal combustion engine object of the invention, the upper face of the piston has surfaces in the form of an inclined plane which extend on either side of the cavity between the bosses, these surfaces being adapted to channel the flush generated by the ends of the bosses towards the center of the cavity.

 According to another characteristic of the diesel internal combustion engine object of the invention, the glow plug is arranged above the intake ducts or exhaust ducts, with a determined inclination relative to the axis of the cylinder .

 The objects, aspects and advantages of the present invention will be better understood from the description given below of an embodiment of

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 the invention, presented by way of nonlimiting example, with reference to the accompanying drawings, in which.

 - Figure 1 is a schematic top view showing the combustion chamber of a diesel internal combustion engine according to the invention Figure 2 is a sectional view along the line ll-ll of Figure 1; - Figure 3 is a top view of the piston shown in Figure 2.

 The embodiment of the invention described in accordance with the figures relates to a four-stroke diesel internal combustion engine of the multicylinder, diesel type, with direct fuel injection and with four valves per cylinder.

 The main body of this internal combustion engine is formed by a cylinder head surmounting a cylinder block 24. A plurality of cylindrical bores or cylinders, identical to cylinder 2 shown in FIG. 2, are arranged in cylinder block 24. Each cylinder 2 houses a piston 3 whose reciprocating movement is intended to be converted into a rotary movement by a connecting rod / crankshaft system not shown.

 In the upper part of the cylinder 2 extends a combustion chamber 1 which is delimited by the upper face of the piston 3, the lower face 13 facing the cylinder head 4 and the walls of the cylinder 2. The lower wall 11 of the cylinder head is mainly in the form of a roof with two slopes, does it have the nails 14 extending substantially parallel to the longitudinal axis of the cylinder head 4.

 Referring to FIG. 1, it can be seen that the cylinder head 4 is traversed transversely for each combustion chamber 1, by two conduits for admitting oxidant gases 5,6 and by two exhaust conduits for burnt gases 9,10. These intake and exhaust ducts extend respectively on either side of the combustion chamber with respect to the longitudinal median plane of the cylinder head, and they open into said combustion chamber by intake orifices 7 / 8 and exhaust

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 11, 12 which are provided with rod valves for controlling the opening thereof.

 The two intake ports 7,8 are arranged through the bottom wall 13 of the cylinder head 4 on the same side with respect to the top edge 14, while the exhaust ports 11 and 12 are arranged through the lower wall of the cylinder head 4 on the side opposite the intake orifices.

 The angle formed between the intake and exhaust valves corresponds substantially to the angle of the roof 13.

 Furthermore, the calibration of the intake orifices is adapted to occupy as much as possible the intake face of the roof 13 at the limit of wall effects, the two intake ducts 5 and 6 which extend substantially parallel to one another. 'other through the cylinder head 4 being further shaped to promote the filling of the combustion chamber 1 with combustion air.

According to the present invention, the bottom wall 13 of the cylinder head 4 also comprises a recess 18 extending substantially parallel to the axis of the cylinder 2. In this recess 18 open a fuel injector 16 and a preheating plug 17 The injector 16 is conventionally connected to a pressure fuel supply circuit that is not shown. The amount of fuel injected either very early in the cycle, in the compression phase or very late in the expansion phase is determined by an electronic engine control system, also not shown, which determines the phasing and the opening time of injector
16 according to the operating conditions of the engine and in particular the load and the speed.

 The recess 18 is formed by a main cavity 22 preferably extending substantially in the axis of the cylinder 2. For implantation purposes, the axis of the recess 18 may, however, deviate from the axis of the cylinder. 2 of a few millimeters. This cavity is delimited in its part

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 upper by a bottom wall 20 or opens the nose of the injector 16 and a side wall 19 of substantially ogival shape truncated or opens the glow plug 17. The lower opening of this cavity can be extended towards the four inter-valve bridges by secondary cavities 21.

 These secondary cavities 21 have the main function of increasing the volume of the recess 18, without increasing the depth of the main cavity 22. Thus, it is possible to have a confinement volume of appropriate size without affecting the compactness of the breech and without reducing the hunting surface.

 Obviously, the number of these secondary cavities is not limiting, it is thus possible to have only three secondary cavities: one extending in the direction of the trigger guard and the other two extending on either side. of the main cavity 22, parallel to the stop 14. Likewise, the shape and dimensions of these cavities are adapted as a function of the space available and the desired confinement volume.

 Furthermore, the shapes of the different secondary cavities 21 surrounding the main cavity 22 are also linked to the shape of the latter. The main cavity 22 can be of circular section (in the case where the injection orifices are arranged and oriented along a cone called a sheet) or else elliptical as shown, the major axis of the ellipse being able to be parallel to the 'ridge 14 or alternatively perpendicular thereto, in this case the arrangement of the jets can be arranged and the angle of the jets adapted locally to exploit the volume thus released. Similarly, the flaring given to the side wall 19 can be reduced to the minimum allowed by molding / machining techniques, so as to achieve a substantially cylindrical shape.

 The fuel injector is mounted through the cylinder head 4 parallel to the axis of the cylinder so that its injection nose opens out substantially in line with the bottom wall 20 of the recess 18.

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According to variant embodiments of the invention, the nozzle of the injector can open out or project laterally from the bottom wall 20.

The dimensions of the recess 18 and those of the ply formed by the fuel injection jets are adapted to one another to avoid any wetting of the side wall 19 directly by the fuel jets, whatever the operating conditions. of the motor. The preheating plug 17 which opens laterally through the wall 19, extends in the cylinder head 4 for example in the axial plane of the cylinder head, either above the intake conduits 5,6 as shown or above the exhaust pipes 9,10.

 The positioning of the preheating plug 17 is also adapted so that the cold start is optimum. It is at a determined distance h from the injector 16 so that it is reached by one of the jets of the injector. The depth H of the recess 18 is chosen so that the aforementioned distance h is appreciably less than two thirds of H (h 2/3) * H). In particular, the preheating plug 17 extends above the secondary cavities 21. This implantation of the preheating plug 17 in the upper part of the recess 18 in the immediate vicinity of the nose of the injector 16, allows then better control cold start and combustion stability in the preheating phases after start.

 Indeed, inside the containment vehicle that the recess 18 constitutes, the aerodynamic movements remain limited in particular in the upper part of the recess 18. It is therefore possible to precisely control the stratification of the fuel mixture.

 In addition, for high-load operations, it is possible to obtain a first combustion phase limited to the recess 18, of very rapid progress close to an isochoric transformation then, when the flame front leaves the recess 18 to reach the cylinder, a second phase of isobaric transformation type. Such a process allows

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 improve the thermodynamic efficiency of combustion for the same maximum cycle temperature, and simultaneously reduce nitrogen oxide and particulate matter emissions.

 It should be noted that the secondary cavities distributed at the periphery of the main cavity 22 have the additional advantage of channeling the swept gases by flushing effect. These gases are thus directed at the outlet of the main cavity 22 and therefore make it possible to promote the rapid propagation of the flame front to the whole of the combustion chamber 1.

 According to the invention, the piston 3 and more particularly its upper face are optimized with respect to the rest of the combustion chamber and more particularly to the recess 18 to allow the engine to operate both in homogeneous mode and in laminate mode .

To do this, the upper face of the piston 3 has a concave recess 30 in the form of a spherical imprint. This cavity 30, coming from foundry and / or obtained after machining, extends substantially in the center of the piston under the recess 18. The circular opening of this cavity 30 has a diameter less than half the diameter of the piston and preferably equal to this one. The cavity 30 is surrounded by two projecting bosses 33. The two bosses 33 are arranged on either side of the cavity
30 along the longitudinal axis of the cylinder head 4 and extend symmetrically with respect to the transverse vertical plane of the cylinder.

 These bosses are arranged at the periphery of the cavity 30 according to an angular sector preferably between 90 and 130. Their shape is complementary to that of the underside 13 of the cylinder head 4, which in particular makes it possible to limit the residual volume of the combustion chamber 1 when the piston 3 is at Top Dead Center, this in order to obtain a rate of adequate gas compression.

 The side walls of the bosses 33 facing the cavity 30 are shaped to extend the spherical imprint; as for the ends 32

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 bosses 33 extending under the intake ports 7,8 and exhaust 11, 12, they are shaped to generate substantial hunting zones oriented towards the center of the cavity. The upper face of the piston 3 also has surfaces 31 in the form of an inclined plane extending on either side of the cavity 30 between the bosses 33. The slope of these surfaces 31 substantially less than that of the ends 32 is suitable to channel the flush generated by these ends 32 towards the cavity 30. Furthermore, these surfaces 31 whose upper edges delimit the opening of the cavity 30, contribute to increasing the volume of the latter without increasing the dimensions of the piston and in particular the thickness of his head.

 The upper face of the piston 13 thus makes it possible to obtain, when the latter is at top dead center, a residual volume for the combustion chamber 1 formed by the recess 18 and the cavity 30 which tends towards a volume of spherical shape with a start of combustion relatively centered.

l'aérodynamique interne que sur la formation et la propagation de la ~Y'' lill lU'-/l 1 1 1 Lil-l 9 LI u combustion. Pour ce qui est de l'aérodynamique interne, l'organisation du mouvement des gaz admis dans la chambre de combustion 1 est centrée dans la cavité 30 ce qui assure le maintien de leur énergie lors de la phase de compression pris du Point Mort Haut combustion, énergie qui se trouve augmentée en fin de compression par les effets de chasse orientés vers le centre de la cavité résiduelle pseudo sphérique que forme alors la chambre de combustion. The shape retained for the piston 3 associated with the recess 18 formed in the cylinder head 4 is particularly suitable for allowing efficient and homogeneous operating modes of operation, both in terms of yield and emission of pollutant, in particular nitrogen oxides and particles. This arrangement therefore has a favorable influence on

internal aerodynamics as on the formation and propagation of the ~ Y '' lill lU '- / l 1 1 1 Lil-l 9 LI u combustion. With regard to internal aerodynamics, the organization of the movement of the gases admitted into the combustion chamber 1 is centered in the cavity 30 which ensures the maintenance of their energy during the compression phase taken from Neutral High combustion point. , energy which is increased at the end of compression by the hunting effects oriented towards the center of the pseudo-spherical residual cavity which then forms the combustion chamber.

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 This intense internal aerodynamics makes it possible to obtain high combustion speeds, therefore an optimal thermodynamic efficiency. Regarding the initiation of combustion and its propagation. In stratified charge, the fuel injected late is concentrated in the recess 18 and partly in the cavity 30 which limits its dispersion in the rest of the cylinder. In homogeneous load, the fuel is injected early and the fuel mixture occupies a residual volume which tends towards a spherical shape benefiting from a substantially homogeneous combustion initialization. The combustion therefore tends to propagate uniformly in the chamber, meeting the walls late in the cycle and at about the same time the walls, this results in limited heat losses and the maintenance of a high combustion speed for a very long time. the cycle.

 Of course, the invention is in no way limited to the embodiments described and illustrated which have been given only by way of nonlimiting examples. On the contrary, the invention includes all the technical equivalents of the means described and their combinations if these are carried out according to the spirit.

Claims (10)

 1. Internal combustion engine with compression ignition comprising a combustion chamber (1) delimited on the one hand by the upper wall of a piston (3) mounted in a cylinder block and on the other hand by the lower wall d '' a cylinder head (4) comprising, on one side of the roof surface (13), two separate inlet openings (7, 8) and on the side opposite to the inlet openings, by two separate openings exhaust (11, 12), characterized in that the cylinder head further comprises a recess (18) opening into the lower wall of the cylinder head (4), a fuel injector (16) arranged parallel to the axis of the cylinder (2 ) and emerging at the top of the recess (18), a preheating plug (17) opening laterally in the recess (18) and in that the piston (3) is provided on its upper wall with a cavity ( 30) extending substantially under said recess (18), said cavity (30) being surrounded by two projecting bosses (33) which extend symmetrically with respect to the transverse plane of the cylinder. 2. Internal combustion engine according to claim 1, characterized in that the recess (18) is formed by a main cavity (22) delimited by a bottom (20) which opens the nose of the injector (16) and a side wall (19), and at least one secondary cavity (21) opening into the lower part of the main cavity (22). 3. Internal combustion engine according to claim 2, characterized in that said main cavity (22) extends substantially in the axis of the cylinder (2). 4. Internal combustion engine according to any one of claims 2 or 3, characterized in that said main cavity (22) is of substantially circular or elliptical section. 5. Internal combustion engine according to any one of claims 2 to 4, characterized in that the secondary cavities (21) extend on either side of the main cavity (22) between the intake orifices ( 7, 18) and / or exhaust. <Desc / Clms Page number 12>

6. Internal combustion engine according to any one of claims 1 to 5, characterized in that said bosses (33) formed on the upper face of the piston (3) around either side of the cavity (30) s '' extend according to an angular sector between 900 and 1300 7. Internal combustion engine according to any one of claims 1 to 6, characterized in that said bosses (33) formed on the upper face of the piston (3) on either side of the cavity (30) have ends extending under the intake and exhaust orifices which are shaped to generate consequent hunting zones oriented towards the center of the cavity (30) 8. Internal combustion engine according to claim 7, characterized in that the upper face of the piston (3) has surfaces (31) in the form of an inclined plane which extend on either side of the cavity (30) between the bosses (33), said surfaces being adapted to channel the flush generated by the ends (32) of the bosses (33) towards the center of the cavity (30). 9. Internal combustion engine according to any one of claims 1 to 8, characterized in that the glow plug (17) extends in the vicinity of a jet from the injector. 10. Internal combustion engine according to any one of claims 1 to 8, characterized in that the glow plug (17) is disposed above the intake ducts (5, 6) or the exhaust ducts (9, 10), with a suitable inclination relative to the axis of the cylinder (2).