PISTON FOR AN INTERNAL COMBUSTION ENGINE SUITABLE FOR THE AERODYNAMIC MOTION OF GAS

Description

technical field

[0001] The present invention relates to the field of pistons for internal combustion engines, in particular a spark-ignition internal combustion engine.

[0002] An internal combustion engine generally comprises at least one cylinder, a piston sliding in that cylinder in a reciprocating rectilinear motion, means for admitting an oxidizer, means for exhausting burnt gases, a combustion chamber, and means for injecting a fuel (propellant). Previous technique

[0003] As is generally accepted, when designing an engine, the constraints of performance, pollutant emissions and consumption are becoming increasingly stringent, and it is therefore necessary to find new solutions to increase the final efficiency of the engine.

[0004] Increasing combustion efficiency is therefore a key factor in limiting pollutant emissions while maintaining or improving performance. To achieve this, utilizing all the fuel present in the combustion chamber with an oxidizer that includes, for example, air at ambient pressure, turbocharged air, or a mixture of air (turbocharged or not) and recirculated exhaust gases is of great importance.

[0005] Indeed, it is necessary that the fuel mixture (oxidizer / fuel) in the combustion chamber be as homogeneous as possible.

[0006] Furthermore, in order to ensure good efficiency and a good combustion speed, it is desirable to have a high level of turbulence, and more specifically a high level of turbulent kinetic energy, at the moment of ignition of the fuel mixture and during its combustion.

[0007] This high level of turbulence can be achieved through the use of a specific intake aerodynamics, Swumble™ (IFP Energies nouvelles, France). This type of aerodynamics is characterized by the fact that the macroscopic movement of the fuel mixture is a combination of swirl (rotational movement of gases in the cylinder around a vertical axis) and tumble (rotational movement of gases in the cylinder along a longitudinal axis).

[0008] Swirl, which is a macroscopic rotational movement of the fuel-air mixture around an axis collinear with the cylinder axis, is characterized by good conservation during the intake process and more specifically during the piston's upward stroke. It is an aerodynamic macroscopic movement commonly used in compression-ignition internal combustion engines, where it is an effective way to homogenize the fuel-air mixture.

[0009] Tumble is also a macroscopic rotational movement of the fuel-air mixture, but around an axis generally perpendicular to the cylinder axis. Its unique characteristic is that it transforms into microscopic aerodynamic movements that create turbulence during the piston's upward stroke. This macroscopic aerodynamic movement is commonly used in spark-ignition internal combustion engines, where it is an effective way to achieve the appropriate combustion speed. Furthermore, this movement is quite sensitive to the combustion chamber geometry and the valve lift profile, both in terms of valve spread and maximum lift height.

[0010] The use of the Swumble™ (IFP Energies nouvelles, France) allows us to benefit from the advantages of the two aerodynamic structures detailed above, thus achieving excellent homogenization and improved combustion speed thanks to a higher level of turbulence during the compression phase than is observed with the best current spark-ignition engines. The Swumble™ is characterized in particular by a continuous movement, throughout the compression stroke via the upward movement of the piston, of the axis of rotation of the aerodynamic gas movement. This axis is initially very inclined within the cylinder at the beginning of compression (strong swirl component) and ends up being essentially aligned with the longitudinal engine axis at the end of compression (strong tumble component).

[0011] These aerodynamic gas movements are generally produced by the shape of the intake manifold and the combustion chamber. However, in order to ensure that the combustion process thus created takes place under the best conditions and to avoid the creation of aerodynamic gas recirculation zones (which could cause localized decreases in turbulence, or even hot spots that could lead to abnormal combustion through auto-ignition, such as knocking or pre-ignition), it is also necessary to optimize the shape of the piston so that it also participates in this aerodynamic gas movement in the combustion chamber.

[0012] Various piston shapes have been developed. For example, French patent application FR2771138 describes a piston that includes deflectors to direct the fuel jet. However, these deflectors also affect the aerodynamic movement of the gas, but are not optimized to ensure such aerodynamic gas movements. Similarly, US patent application 6725828 describes a piston adapted for a direct-injection, spark-ignition internal combustion engine operating under stratified charge. The shape of the piston head is adapted for fuel injection, but also generates aerodynamic gas movement; however, this piston shape is not optimized to ensure swirl, tumble, or Swumble™-type aerodynamic gas movements. As another example, utility model CN ​​20787786 relates to a piston with a central hollow and peripheral bumps, designed to optimize the tumble rate and turbulent kinetic energy.However, this shape does not allow for efficient aerodynamic displacement of the gas towards the exhaust during the piston's upward movement towards top dead center, and could also generate hot spots. Other pistons with valve recesses and inclined surfaces are known from JP 2018 204600 A, US 2001 / 018904 A1, or DE19928108 A1.

[0013] Furthermore, conventionally, the piston head may include at least one recess for an intake valve and at least one recess for an exhaust valve, to allow the intake and / or exhaust valves to open at top dead center. However, these recesses create aerodynamic zones where gases can recirculate into the combustion chamber. Therefore, it is important to optimize the piston shape to avoid the formation of recirculation zones for pistons with recesses. Summary of the invention

[0014] The present invention aims to facilitate the displacement of the aerodynamic movement of the gas in the combustion chamber towards the exhaust during the upward stroke of the piston, and to prevent any aerodynamic recirculation zone that could create a hot spot or a localized area of ​​low turbulent kinetic energy in the combustion chamber. To this end, the invention relates to an internal combustion engine piston, which includes recesses for intake and exhaust valves, and a connecting surface between the intake and exhaust valve recesses. This connecting surface comprises a portion inclined towards at least one exhaust valve recess. This inclined portion optimizes the aerodynamic movement of the gas and limits aerodynamic recirculation zones.

[0015] The invention relates to an internal combustion engine piston, said piston comprising at least one recess for an intake valve and at least one recess for an exhaust valve, said piston having a connecting surface between said at least one recess for an intake valve and said at least one recess for an exhaust valve.Said connecting surface comprises an inclined portion, said inclined portion being secant to said at least one recess for an exhaust valve, the deepest area of ​​the inclined portion being at the level of the intersection with the at least one recess for an exhaust valve, and, in a plane perpendicular to the axis of said piston, the median axis of said inclined portion which separates said at least one recess for an intake valve and said at least one recess for an exhaust valve is offset with respect to a median axis of said piston which separates said at least one recess for an intake valve and said at least one recess for an exhaust valve.

[0016] According to one embodiment, said inclined portion is flat.

[0017] Advantageously, said connecting surface not included in said inclined portion is flat and perpendicular to the axis of said piston.

[0018] According to one embodiment, said inclined portion is concave, the axis or center of said concavity of the inclined portion not intersecting the axis of said piston.

[0019] Advantageously, said connecting surface not included in said inclined portion is concave, the axis or center of said concavity of said connecting surface being secant to the axis of said piston.

[0020] According to one implementation, said piston includes two recesses, each for an intake valve.

[0021] According to one aspect, the piston comprises two recesses, each for an exhaust valve.

[0022] According to one feature, the angle of inclination of said inclined portion with respect to a plane perpendicular to the axis of the piston is less than 25°, preferably between 2 and 15°. According to one embodiment, said inclined portion intersects with said at least one exhaust valve recess with a radius of curvature between 1 and 500 mm, preferably between 5 and 50 mm.

[0023] According to one embodiment, at the intersection between said inclined portion and said at least one recess for an exhaust valve, the height between said inclined portion and said connecting surface is less than or equal to 10 mm, preferably less than or equal to 5 mm.

[0024] According to one embodiment, said inclined portion has a substantially rectangular shape in a plane perpendicular to the axis of the piston, preferably a substantially square shape.

[0025] Furthermore, the invention relates to an internal combustion engine, in particular a spark-ignition internal combustion engine, the engine comprising at least one cylinder, each cylinder comprising a piston according to one of the preceding characteristics, said piston sliding in said cylinder, at least one intake port provided with an intake valve and at least one exhaust port provided with an exhaust valve, each cylinder comprising a combustion chamber, said combustion chamber being delimited by the upper face of said piston, by the internal surface of said cylinder and by said cylinder head.

[0026] According to one embodiment, said cylinder head has a roof shape.

[0027] According to one implementation, said at least one intake duct includes means for generating an aerodynamic movement of the gas within said cylinder around an axis substantially collinear with the axis of said cylinder and / or around an axis substantially perpendicular to the axis of said cylinder.

[0028] Furthermore, the invention relates to the use of an internal combustion engine according to one of the preceding characteristics for a Miller cycle or an Atkinson cycle.

[0029] Other features and advantages of the device according to the invention will become apparent from the following description of non-limiting examples of embodiments, with reference to the figures attached and described below. List of figures

[0030] There figure 1 illustrates a three-dimensional view of a piston according to a prior art. figure 2 illustrates a cross-sectional view of a piston according to a prior art. figure 3illustrates a three-dimensional view of a piston according to one embodiment of the invention. figure 4 illustrates a cross-sectional view of a piston according to one embodiment of the invention. figure 5 illustrates the aerodynamic movement of gas in the combustion chamber for a piston according to the prior art. figure 6 illustrates an aerodynamic movement of gas in the combustion chamber for a piston according to an embodiment of the invention. Description of the implementation methods

[0031] The invention relates to an internal combustion engine piston, particularly for a spark-ignition internal combustion engine. The piston has, on its crown—that is, on the face of the piston facing the cylinder head of the internal combustion engine (called the top face of the piston)—at least one recess for an intake valve and at least one recess for an exhaust valve. The recesses are cutouts in the top face of the piston to allow the passage of the intake and / or exhaust valves. Generally, the recesses for the intake valves can be different from those for the exhaust valves. These recesses allow for a compact design by reducing overall size and enable the intake and exhaust valves to open at top dead center of the piston.

[0032] Furthermore, the upper face of the piston includes a connecting surface between at least one intake valve recess and at least one exhaust valve recess. The connecting surface may be flat or curved.

[0033] According to the invention, the connecting surface comprises a portion inclined towards at least one exhaust valve recess. This portion is inclined relative to a plane perpendicular to the piston axis. In other words, at least a part of the connecting surface is inclined, and its inclination is directed towards at least one exhaust valve recess. This inclined portion allows the aerodynamic movement of the gas to be directed towards the exhaust.

[0034] Furthermore, the inclined portion intersects with at least one exhaust valve recess. The deepest point of the inclined portion is at the intersection with at least one exhaust valve recess. Thus, the exhaust valve recess does not create a gas recirculation zone in the combustion chamber.

[0035] Furthermore, in a plane perpendicular to the piston axis, a median axis of the inclined portion that separates at least one intake valve recess on one side and at least one exhaust valve recess on the other is offset from a median axis of the piston that separates at least one intake valve recess on one side and at least one exhaust valve recess on the other. A median axis is defined as an axis that is equidistant from opposite points or sides of the shape under consideration (piston shape or inclined portion). In other words, in a plane perpendicular to the axis of the piston (which may correspond to a top view of the piston when it is arranged vertically), the inclined portion is not centered with the piston, and this off-centering is arranged in a direction that passes through at least one intake valve recess and at least one exhaust valve recess.Because of the intersection between the inclined portion and the at least one exhaust valve recess, and because of this off-centering, the median axis of the inclined portion is closer to the at least one exhaust valve recess than to the at least one intake valve recess.

[0036] According to one embodiment of the invention, the inclined portion can be flat.

[0037] In this embodiment, the connecting surface not included in the inclined portion may be flat and may be perpendicular to the piston axis. The term "connecting surface not included in the inclined portion" refers to the connecting surface between at least one intake valve recess and at least one exhaust valve recess, excluding the inclined portion. This design of the connecting surface is simple.

[0038] Alternatively, the inclined portion can be concave (curved, lens-shaped). Preferably, the concavity of the inclined portion can be formed by a portion of a cylinder or a portion of a sphere. Due to the off-center nature of the inclined portion, the axis (e.g., in the case of a portion of a cylinder) or the center (e.g., in the case of a portion of a sphere) of the concavity does not intersect the piston axis. In other words, the center or axis of the concavity of the inclined portion is offset from the piston axis. The concavity of the inclined portion improves combustion within the combustion chamber by optimizing the shape of its volume.

[0039] In this embodiment, the connecting surface not included in the inclined portion can be concave (curved, lens-shaped). Preferably, the concavity of the connecting surface can be formed by a portion of a cylinder or a portion of a sphere. The axis (for example, in the case of a portion of a cylinder) or the center (for example, in the case of a portion of a sphere) of the concavity intersects the axis of the piston.

[0040] In other words, the center of the concavity of the connecting surface belongs to the axis of the piston, or the axis of the concavity of the connecting surface belongs to the axis of the piston.

[0041] For this latter implementation, the radius of concavity (the radius of the cylinder or sphere, as applicable) of the connecting surface can be greater than the radius of concavity (the radius of the cylinder or sphere, as applicable) of the inclined portion. The radii of concavity can be significant relative to the piston size. As a non-limiting example, the radii can be several hundred millimeters; for instance, they can range from 100 to 1000 mm, and preferably from 200 to 600 mm. Thus, the curvature of the connecting surface is greater for the inclined portion, which favors the direction of aerodynamic gas flow towards the exhaust.

[0042] Alternatively, for this embodiment, the connecting surface not included in the inclined portion can be flat, and can be perpendicular to the axis of the piston.

[0043] Preferably, the connection surface should have no protruding elements. Indeed, protruding elements promote changes in the aerodynamic movement of the gas.

[0044] According to one embodiment of the invention, the piston may include two intake valve recesses. Thus, the piston is suitable for an internal combustion engine with two intake valves.

[0045] Alternatively or cumulatively, the piston may include two exhaust valve recesses. Thus, the piston is suitable for an internal combustion engine with two exhaust valves.

[0046] Preferably, the piston may include two intake valve recesses and two exhaust valve recesses. Thus, the piston is suitable for an internal combustion engine with four valves. In this embodiment, the two intake valve recesses may be close to each other, and the two exhaust valve recesses may be close to each other.

[0047] In order to optimize the direction of the aerodynamic movement of the gas in the combustion chamber, the angle of inclination of the inclined portion with respect to a plane perpendicular to the axis of the piston may be less than 25°, and may preferably be between 2 and 15°.

[0048] When the inclined portion is flat, the angle of inclination corresponds to the angle formed between the plane of the inclined portion and a plane perpendicular to the axis of the piston. When the inclined portion is concave or not flat, the angle of inclination can be defined, in a cutting plane that passes through an intake port and an exhaust port and is parallel to the axis of the piston, by the angle formed between a line passing through the highest and lowest points of the inclined portion, and a line belonging to a plane perpendicular to the axis of the piston.

[0049] According to one embodiment of the invention, the inclined portion can intersect at least one exhaust valve recess with a radius of curvature between 1 and 500 mm, preferably between 5 and 50 mm. This radius of curvature avoids excessively sharp intersections that could cause areas of gas recirculation in the combustion chamber.

[0050] According to one aspect of the invention, at the intersection between the inclined portion and at least one recess for an exhaust valve, the height of the inclined portion (the dimension of the inclined portion along a direction parallel to the piston axis) relative to the connecting surface not included in the inclined portion may be less than or equal to 10 mm, preferably less than or equal to 5 mm. This height thus ensures an optimized intersection with the at least one recess for the exhaust valve.

[0051] According to one embodiment of the invention, in a plane perpendicular to the piston axis, the inclined portion can have substantially the shape of a quadrilateral, preferably a rectangle or a trapezoid, for example, substantially a square. Preferably, at least one side of the quadrilateral (most preferably two sides) can be parallel to a median axis of the piston that separates, on the one hand, at least one intake valve recess and, on the other hand, at least one exhaust valve recess. When the piston has two exhaust valve recesses, one side of the quadrilateral can correspond to a straight line segment between the two exhaust valve recesses. This shape provides a good surface area for directing the aerodynamic movement of the gas.

[0052] For this embodiment, the connecting surface not included in the inclined portion can have substantially the shape of a U in a plane perpendicular to the axis of the piston.

[0053] Preferably, the inclined portion can be symmetrical about a plane containing the piston axis and an axis perpendicular to the median axis of the inclined portion. This axis separates at least one intake valve recess on one side from at least one exhaust valve recess on the other. This symmetry ensures piston symmetry and good gas distribution, particularly when two exhaust valve recesses are provided. It should be noted that the axis of symmetry is perpendicular to the median axis of the inclined surface separating at least one intake valve recess on one side from at least one exhaust valve recess on the other. This axis of symmetry is also perpendicular to the median axis of the piston which separates on one side at least one intake valve recess, and on the other side at least one exhaust valve recess.

[0054] According to one embodiment of the invention, in a plane perpendicular to the piston axis, the inclined portion can represent at least 40% and at most 80% of the total connecting surface. Thus, a large part of the connecting surface serves to direct the aerodynamic movement of the gas.

[0055] The angled portion can be produced directly during piston manufacturing, for example by casting or additive manufacturing. Alternatively, the angled portion can be produced by machining.

[0056] THE Figures 1 And 2 illustrate, schematically and without limitation, a piston according to a prior art. figure 1 is a three-dimensional view of the piston, and the figure 2is a cross-sectional view of the piston along a plane passing through an intake valve recess and an exhaust valve recess. Piston 1 has two intake valve recesses 2. Piston 1 also has two exhaust valve recesses 3. A flat mating surface 4 is provided between the intake valve recesses 2 and the exhaust valve recesses 3. On the figure 1 , we have represented the axis of the piston AP, here substantially vertical, as well as the median axis AM1 of the piston 1, this median axis AM1 of the piston 1 separates on one side the recesses 2 for intake valve, and on the other side the recesses 3 for exhaust valve.

[0057] THE figures 3 And 4 illustrate, schematically and without limitation, a piston according to one embodiment of the invention. figure 3 is a three-dimensional view of the piston, and the figure 4This is a cross-sectional view of the piston along a plane passing through an intake valve recess and an exhaust valve recess. The piston 1 has two intake valve recesses 2. The piston 1 also has two exhaust valve recesses 4. A connecting surface 4 is provided between the intake valve recesses 2 and the exhaust valve recesses 3. The connecting surface 4 has at least one inclined portion 5 directed towards the exhaust valve recesses 3. In the illustrated embodiment, viewed from above (along a plane perpendicular to the piston axis), the inclined portion is substantially rectangular, and the remaining part of the connecting surface is substantially U-shaped. The inclined portion 5 is concave, and the remainder of the connecting surface 4 is flat.

[0058] On the figure 3The axis of piston AP, shown here as approximately vertical, is represented, as is the median axis AM1 of piston 1. This median axis AM1 separates the intake valve recesses 2 on one side and the exhaust valve recesses 3 on the other. Furthermore, the median axis AM5 of the inclined portion is shown, which separates the intake valve recesses 2 on one side and the exhaust valve recesses 3 on the other. This median axis AM5 of the inclined portion 5 is offset by a distance d from the median axis AM1 of piston 1. In addition, an axis of symmetry AS5 of the inclined portion 5 is shown, which defines a plane of symmetry between piston 1 and the axis of piston AP.

[0059] On the figure 4The piston axis AP is represented, along with an axis PP perpendicular to the piston axis AP (and therefore belonging to a plane perpendicular to the piston axis). Reference numeral 6 designates the intersection between the inclined portion 5 and the exhaust valve recesses 3. The height between the intersection 6 and the connecting surface not included in the inclined portion 4 is denoted h. Furthermore, the angle of inclination of the inclined portion 5 with respect to a plane perpendicular PP to the piston axis is denoted α. This angle is defined with respect to an axis of inclination AI5 which passes through the cutting plane of the figure 4 by the highest point and the lowest point of the inclined portion 5.

[0060] Furthermore, the present invention relates to an internal combustion engine comprising at least one cylinder, each cylinder being equipped with: of at least one intake device advantageously equipped with an intake valve, for the admission of a gas into the cylinder, of at least one exhaust device, for evacuating the burnt gases from the cylinder, the exhaust device is advantageously equipped with an exhaust valve, a cylinder head comprising at least at least one intake device and at least one exhaust device, of a piston having a reciprocating rectilinear translational movement in the cylinder to generate mechanical energy from combustion (by rotation of a crankshaft), the piston conforming to one of the variants or combinations of variants described above, and of means for fuel injection, to generate combustion.

[0061] Within the cylinder, a combustion chamber is formed by the upper surface of the piston, the cylinder wall, and the cylinder head.

[0062] According to one embodiment, the fuel injection means can be direct injection means, that is to say, the fuel injection means are disposed directly in the cylinder.

[0063] Alternatively, the fuel injection means may be indirect injection means, that is, the fuel injection means are disposed in the intake device.

[0064] According to one embodiment of the invention, the internal combustion engine is a spark-ignition engine. In this case, the engine further comprises at least one spark plug to generate the combustion of the gas and fuel mixture.

[0065] Alternatively, the internal combustion engine is a compression-ignition engine. In this case, the engine does not have a spark plug to generate the combustion of the gas and fuel mixture.

[0066] The internal combustion engine can have a plurality of cylinders, including 3, 4, 5 or 6 cylinders.

[0067] Preferably, the combustion engine can be a four-valve-per-cylinder engine (two intake valves and two exhaust valves).

[0068] According to one embodiment of the invention, the cylinder head can have a substantially roof-like shape (triangular "in volume"). This cylinder head shape allows for an optimized combustion chamber shape and promotes gas movement compared to a flat cylinder head shape.

[0069] According to one embodiment of the invention, the cylinder may include means for generating an aerodynamic movement of the gas within the combustion chamber around an axis substantially collinear with the axis of the cylinder (corresponding to the axis of the piston), thus generating a swirling motion.

[0070] Alternatively or additionally, the cylinder may include means for generating an aerodynamic movement of the gas within the combustion chamber around an axis substantially perpendicular to the axis of the cylinder (corresponding to the axis of the piston), thus generating a tumble motion.

[0071] Preferably, the cylinder may include means for generating an aerodynamic movement of the gas within the combustion chamber around an axis substantially collinear with the cylinder axis, and around an axis substantially perpendicular to the cylinder axis, thus generating a Swumble™ motion. The present invention is particularly suited for this embodiment, given that the piston allows for good displacement of the turbulent gas motion, especially towards the exhaust during the upward movement of the piston towards top dead center.

[0072] For this embodiment, the intake device can be provided to generate tumble, swirl or Swumble™ movements.

[0073] For example, the intake device may include an intake duct with a springboard shape and / or a convergence of the intake duct passage section, and / or an inclination of the intake duct and / or a mask and / or a rotation of the end of the intake duct, etc.

[0074] The intake duct may in particular conform to one of the intake ducts described in the patent applications: FR3080888 (WO2019 / 211040), FR3091906 (WO2020 / 151985), FR3095235 (WO2020 / 212115), FR3095236 (WO2020 / 212117), and FR3095237 (WO2020 / 212112).

[0075] Furthermore, the present invention relates to the use of an internal combustion engine according to one of the variants or combination of variants described above according to a Miller cycle or an Atkinson cycle.

[0076] The Miller cycle is a thermodynamic cycle characterized by the closure of the intake valve(s) before the piston reaches bottom dead center during the intake phase. This increases the geometric compression ratio while maintaining the same effective compression ratio, resulting in greater work recovery through an increased expansion ratio and cooling of the intake charge. The intake device according to the invention is particularly well-suited for use in the Miller cycle over a wide operating range thanks to the generation of an aerodynamic Swumble™-type gas movement.

[0077] The Atkinson cycle is the standard thermodynamic cycle used in combustion engines.

[0078] The internal combustion engine according to the invention can be used in the field of embedded applications, such as road, maritime or aeronautical fields, or in the field of stationary installations, such as a generator set.

[0079] As can be understood, the invention is not limited to the forms of embodiment of the piston described above by way of example, but rather encompasses all variant embodiments. Comparative example

[0080] The characteristics and advantages of the piston according to the invention will become clearer upon reading the application example below.

[0081] For this comparative example, the aerodynamic movement of the gas in the combustion chamber of a cylinder equipped with a piston, according to an embodiment of the invention (according to the embodiment of the CFD), is compared using computational fluid dynamics (CFD) simulation. figures 3 And 4 ), with the aerodynamic movement of the gas in the combustion chamber of a cylinder equipped with a piston according to a prior art (according to the prior art of Figures 1 And 2 ), the intake and exhaust being identical for both simulations, in particular the intake duct is configured to generate an aerodynamic Swumble™ type gas movement.

[0082] There figure 5This is a schematic cross-sectional view of the combustion system at the end of the compression stroke at top dead center with a piston according to the prior art. In this figure, the upper face of the piston 1 is shown (in white) with a recess 2 for an intake valve, a recess 3 for an exhaust valve, and a flat connecting surface 4. Also shown is a roof-shaped cylinder head 8 with an intake valve 9 (in white) in an intake port 12, and an exhaust valve 10 (in white) in an intake port 13. In this figure, it can be seen that the aerodynamic movement of the gas (streamlines in gray) is confined to the center of the combustion chamber 7 and does not penetrate below the exhaust valves 3, creating a high-temperature zone 11.

[0083] There figure 6is a schematic and non-limiting cross-sectional view of the combustion system at the end of the compression stroke at top dead center with a piston according to an embodiment of the invention. In this figure, the upper face of the piston 1 is shown (in white) with a recess 2 for an intake valve, a recess 3 for an exhaust valve, and a connecting surface with a concave inclined portion 5. A roof-shaped cylinder head 8 is also shown with an intake valve 9 (in white) in an intake port 12, and an exhaust valve 10 (in white) in an intake port 13. In this figure, it can be seen that the aerodynamic movement of the gas (streamlines in gray) is much more developed and extends under the exhaust valves, eliminating the high-temperature zone (zone 11 is significantly reduced compared to the figure 5 ).

[0084] Thus, the invention allows good displacement of the aerodynamic movement of the gas in the combustion chamber towards the exhaust during the upward movement of the piston towards top dead center, and limits the areas of high temperatures.

Claims

1. Piston for an internal combustion engine, said piston (1) comprising at least one recess for an intake valve (2) and at least one recess for an exhaust valve (3), said piston (1) comprising a connecting surface (4) between said at least one recess for an intake valve (2) and said at least one recess for an exhaust valve (3), said connecting surface (4) comprising an inclined portion (5), said inclined portion (5) being secant to said at least one recess for an exhaust valve (3), and in a plane perpendicular to the axis of said piston (AP), a median axis of said inclined portion (AM5), which separates said at least one recess for an intake valve (2) and said at least one recess for an exhaust valve (3), being offset with respect to a median axis of said piston (AM1) which separates said at least one recess for an intake valve (2) and said at least one recess for an exhaust valve (3), characterized in that the deepest zone of the inclined portion is at the level of the intersection with the at least one recess for an exhaust valve.

2. Piston for an internal combustion engine according to Claim 1, wherein said inclined portion (5) is planar.

3. Piston for an internal combustion engine according to Claim 2, wherein said connecting surface not included in said inclined portion is planar and perpendicular to the axis of said piston (AP).

4. Piston for an internal combustion engine according to Claim 1, wherein said inclined portion (5) is concave, the axis or the centre of said concavity of the inclined portion (5) being non-secant with the axis of said piston (AP).

5. Piston for an internal combustion engine according to Claim 4, wherein said connecting surface not included in said inclined portion is concave, the axis or the centre of said concavity of said connecting surface being secant with the axis of said piston (AP).

6. Piston for an internal combustion engine according to one of the preceding claims, wherein said piston comprises two recesses for an intake valve (2).

7. Piston for an internal combustion engine according to one of the preceding claims, wherein said piston comprises two recesses for an exhaust valve (3).

8. Piston for an internal combustion engine according to one of the preceding claims, wherein the angle of inclination (α) of said inclined portion (5) with respect to a plane perpendicular to the axis of the piston (AP) is less than 25°, and it is preferably comprised between 2 and 15°.

9. Piston for an internal combustion engine according to one of the preceding claims, wherein said inclined portion (5) is secant with said at least one recess for an exhaust valve (3), with a radius of curvature comprised between 1 and 500 mm, preferably between 5 and 50 mm.

10. Piston for an internal combustion engine according to one of the preceding claims, wherein, at the intersection (6) between said inclined portion (5) and said at least one recess for an exhaust valve (3), the height (h) between said inclined portion (5) with respect to said connecting surface is less than or equal to 10 mm, preferably less than or equal to 5 mm.

11. Piston for an internal combustion engine according to one of the preceding claims, wherein said inclined portion (5) has a substantially rectangular shape in a plane perpendicular to the axis of the piston (AP), preferably a substantially square shape.

12. Internal combustion engine, notably a controlled-ignition internal combustion engine, the engine comprising at least one cylinder, each cylinder comprising a piston (1) according to one of the preceding claims, said piston (1) sliding in said cylinder, at least one intake duct (12) provided with an intake valve (9) and at least one exhaust duct (13) provided with an exhaust valve (10), each cylinder comprising a combustion chamber (7), said combustion chamber (7) being delimited by the upper face of said piston (1), by the internal surface of said cylinder and by said cylinder head.

13. Internal combustion engine according to Claim 12, wherein said cylinder head has a roof shape (8).

14. Internal combustion engine according to one of Claims 12 and 13, wherein said at least one intake duct (12) comprises means for generating an aerodynamic movement of the gas within said cylinder about an axis substantially collinear with the axis of said cylinder and / or about an axis substantially perpendicular to the axis of said cylinder.

15. Use of an internal combustion engine according to one of Claims 12 to 14 for a Miller cycle or an Atkinson cycle.