EP1714023A1

EP1714023A1 - Direct-injection internal combustion engine

Info

Publication number: EP1714023A1
Application number: EP05726421A
Authority: EP
Inventors: Guillaume Gautier; Rafik Ben Dakhlia
Original assignee: Peugeot Citroen Automobiles SA
Current assignee: PSA Automobiles SA
Priority date: 2004-02-13
Filing date: 2005-02-11
Publication date: 2006-10-25
Also published as: WO2005078270A1; FR2866393B1; FR2866393A1

Abstract

An internal combustion engine including a housing (1) with a cylindrical bore (3), a cylinder head (4), a piston (5) provided in the cylinder, and a fuel injector (18) controlled by electronic control means, wherein said injector (18) injects fuel in a first sheet and/or a separate second sheet, said piston includes a cavity (22) for co-operating with said sheets when the piston (5) reaches top dead centre, and said cavity (22) is shaped in such a way that the two sheets do not cause direct interference when fuel is injected simultaneously in said first and second sheets.

Description

DIRECT INJECTION INTERNAL COMBUSTION ENGINE

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

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

Are known, for example from documents US 5 150 677 or US 5 868 112, a direct fuel injection engine comprising a casing in which are arranged several cylinders, pistons sliding in the cylinders and a cylinder head closing the upper end of the housing.

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 of the cylinders, this injector opening in the lower part of the cylinder head facing the cylinder, approximately in the center of the latter.

The pistons are shaped to present on their upper face oriented towards the cylinder head, a central cavity in the shape of a profiled bowl surrounded by an annular flushing zone.

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 wall cylindrical upper part of the housing oriented towards the cylinder head and the upper surface of the piston.

On the shape of this combustion chamber depends the quality of the preparation of the fuel mixture and from there, the quality of the combustion. This shape is therefore carefully studied in particular with respect to the injected fuel jet and the positioning of the intake and exhaust valves.

Numerous forms of profile of the bowl formed in the head of the piston have been proposed both for the purpose of improving the performance of the piston and that of limiting the emissions of smoke linked to poor elimination of soot.

In general, the diesel combustion chambers with direct injection under high pressure or "common rail" currently used, have the following features:

- The bowl of the piston is axisymmetric and of vertical axis: it comprises a central part or raised stud connecting to a lateral or external wall which can be vertical or have a concavity. The central part may be in the form of an alpha angle cone, as shown in the patents mentioned above; exceptionally, the side 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 beta angle cone, called tablecloth angle, and with an 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 made near top dead center (TDC), that is to say near the plane of the cylinder head;

- The fuel axes intersect the outer wall of the bowl when the piston is in top dead center, as seen for example in the figures in document US4635597, and this results in a swirling movement with a horizontal axis intended to deflect the mixture of first down then the center of the bowl.

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

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 layers of fuel jets (at least four per layer), called twin-layer injector.

Reference may 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 according to a first ply called "open angle ply" and a second ply called "narrow angle ply". The bi-ply injector allows operation with a single ply (preferably ply 1) mainly under partial load (or lightly charged engine operating point) and thus allows the use of low permeability to provide gain in terms of pollutant emissions. In a second type of operation, mainly at high speed and high load, the two layers of the injector are open and make it possible to improve the performance of the engine.

The proposed invention therefore consists in proposing in the context of an engine equipped with two-ply injector, an optimized shape of the cavity formed in the piston adapted at the same time to an operation of the injector with the two plies open. (heavily loaded operating point) and low load single-layer operation.

The invention aims to improve the operation and performance of an engine, by optimal use of the volume of the cavity at all speeds. The invention more precisely consists in optimizing the shape of the cavity to allow optimum distribution of the fuel coming from a twin-ply injector.

The internal combustion engine according to the invention comprises a casing comprising 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 according to a first ply and / or a separate second ply and in that the piston has a cavity intended to cooperate with said plies during passage piston near the top dead center, the cavity being shaped so that the two layers do not interfere directly when the fuel injection is operated simultaneously according to the first and the second layers. According to another characteristic of the engine which is the subject of the invention, the first and second fuel layers are substantially conical and substantially coaxial, the first layer enveloping the second layer.

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

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

According to another characteristic of the engine which is the subject of the invention, the second ply has an angle at the top (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 head of the piston 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 which is the subject of the invention, the step extending in the cavity formed in the head of the piston is arranged so as to be able to be impacted by said first ply.

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

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

According to another characteristic of the engine which is the subject of the invention, the cavity formed in the head of the piston satisfies the relationship: 5% <((Dbol - Dcol) / Dbol * 100) <9%, with Dbol: maximum diameter of the groove annular; Dcol: minimum diameter at the step.

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:

- Figure 1 shows a schematic and partial sectional view of an internal combustion engine;

- Figures 2, 3a and 3b show schematic sectional views of a two-ply injector; - Figure 4 is a partial view in axial section specifying the shape of a piston according to the invention;

- Figure 5 is a detail view of the piston shown in Figure 4 specifying the impact zones of the fuel jets, when the piston is near the top dead center.

In FIG. 1, an engine casing 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 bottom surface opposite the cylinder head 4 a combustion chamber 7. The cylinder head 4 comprises intake gas intake means formed by at least one conduit 8 opening into the roof of the chamber 7 through an opening 9, and a control valve 10 capable of being actuated between a closed position of obturation of the opening 9 and an open gas intake position. The valve 10 comprises a control rod 11 and a closure head 12 of frustoconical shape, the inclined peripheral surface of which comes into contact with a corresponding surface of the opening 9 forming a valve seat to close the opening 9.

The cylinder head 4 comprises exhaust means for the burnt gases formed by at least one exhaust duct 13 opening into the roof of the chamber 7 through an opening 14 capable of being closed by a control valve 15 comprising an actuating rod 16 and a shutter head 17.

The cylinder head 4 also comprises a fuel injection means formed by a piloted injector 18 receiving the fuel at an external inlet at a suitable pressure and having at one end projecting from the chamber 7 an injection head 19 capable of spraying the fuel in the form of fine droplets in the chamber 7 at the appropriate time determined by the not shown engine control system, which notably controls the injection time and the injection duration (i.e. the quantity injected) .

The piston 5 comprises a head 20 whose upper surface 6 facing the cylinder head forms the lower 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 includes a lug of fixing comprising an axis on which is fixed the head of a connecting rod making it possible to transform the translational movement of the piston 5 into the rotary movement of a crankshaft, not shown in FIG. 1. During the rotation of the engine crankshaft, the piston 5 moves between a low neutral position, or PMB, far from the cylinder head 4, and a high neutral position, 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 the bi-ply type has a first series of holes 191 intended to produce a first conical sheet of fuel NI, of angle at the betal apex. This NI sheet is formed, for example, by at least four holes and therefore four fuel jets.

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

The first NI ply has a betal 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 cylinder head 4. The second N2 ply has a beta2 angle between 90 and 150 degrees, and the junction point of its jets is located at a distance D22 from the cylinder head gasket plane 4. The distances D21 and D22 are dependent on the geometry of the injector and its location in the cylinder head.

There are different possibilities of placing the holes 191 of the first sheet NI and the holes 192 of the second sheet N2, relative to each other. A first achievement, cf. Figure 3a is to arrange the holes so that the jets are superimposed. In one second embodiment, cf. Figure 3b, the holes are staggered.

The injector 18 is shaped to be able to selectively control by the engine control system to operate the fuel injection according to one and / or the other of the layers NI, N2 and this, according to the operating point of the engine. Thus at high load the fuel is injected simultaneously via the two layers NI and N2, while at partial load, the fuel is injected in the form of the single layer NI.

Referring to FIG. 4, the upper surface 6 of the piston 5 comprises a central cavity 22. In the example illustrated, this cavity 26 is surrounded by a substantially flat circular hunting zone 23 facing the lower surface of the cylinder head 4. This hunting zone presented extending perpendicular to the axis of the piston could obviously not be. In the embodiment of FIG. 4, taken by way of nonlimiting 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 the first groove 25, a second annular groove 26 and between the two, a convex connection zone 27, also called step (or reentrant) and a bottom wall projecting from a central protuberance 28.

This central protuberance 28 is, for example, of conical shape and its rounded top is shaped to be at a distance D1 (generally between 4mm and 6mm) from the joint plane of the cylinder head 4 when the piston 5 is at TDC. This central conical protuberance 28 is adapted to have an angle at the apex substantially similar to beta2 and a positioning adapted so that the second ply N2 comes to sweep it and is thus directed towards the bottom of the groove 26. The step 27 is positioned to receive the first NI tablecloth. 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 step 27 is Dcol. Finally, Hbol represents the maximum depth of the cavity 22 relative to the opening 24.

Referring to Figure 5, we see the interaction of the two fuel layers NI and N2 and the cavity 22. This situation corresponds to a high load operation where the quantity of fuel injected is the most important and where the fuel is injected through the two layers NI and N2, in a superimposed configuration.

To promote the preparation of the air / fuel mixture necessary for the proper conduct of combustion, it is important that the layer N2 well fill the annular groove 26 where the air / fuel mixture operates and does not directly interfere with the layer NI. It is also important that the NI tablecloth is well distributed both to the hunting area and to the center of the combustion chamber. This distribution is ensured by the rounded step 27 which receives the NI sheet and limits the penetration of the NI sheet in the direction of the annular cavity 26.

In order to optimize this fuel distribution in a bi-layer 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 allowing the desired wealth to be obtained while allowing the two layers of fuel jets NI and N2 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 flushing zone 23 during expansion, that is to say when the piston 5 descends, the percentage of step 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 NI sheet is present. This configuration is generally used for operating the engine under partial load. The angles of opening of this ply proposed by the Applicant make it possible to inject the fuel in accordance with a concept known as conventional where an injector with a single ply is mounted.

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

Claims

1. Internal combustion engine comprising a casing (1) comprising 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 according to a first ply and / or a separate second ply (NI, N2) and in that said piston includes 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 so that the two layers do not interfere directly when the fuel injection is operated simultaneously according to said first and said second layers ( N1, N2) and in that said cavity (22) comprises an annular groove (26) delimited towards the opening (24) of the cavity (23) by a step (27) and a central protuberance (28) facing the injector (18).

2. Internal combustion engine according to claim 1, characterized in that said first and second plies (NI, 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 (NI) extends at a distance (D21) from the joint plane of the cylinder head (4) substantially less than the distance (D22 ) separating the top of said second ply (N2) at said joint plane of the cylinder head (4).

4. Internal combustion engine according to claim 2, characterized in that said first ply (NI) has an apex angle (betal) between 140 ° and 175 °.

5. Internal combustion engine according to claim 2, characterized in that said second ply (N2) has an angle at the top (beta2) between 90 ° and 160 °.

6. Internal combustion engine according to any one of the preceding claims, characterized in that said step (27) is arranged so as to be able to be impacted by said first ply (NI).

7. Internal combustion engine according to any one of the preceding claims, 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 layer (N2).

8. Internal combustion engine according to any one of the preceding claims, 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).

9. Internal combustion engine according to any one of the preceding claims, 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 step (27).