FR3020836A1 - INTERNAL COMBUSTION ENGINE OF POLYFUEL TYPE WITH DIRECT INJECTION WITH COMMAND IGNITION. - Google Patents

Abstract

The invention relates to a direct-injection direct-injection poly-fuel combustion engine operating on an engine cycle comprising a compression phase and comprising: - a cylinder (2), - an exhaust pipe (14) combustion gases produced in the cylinder (2) of the engine in communication with the cylinder (2) by means of an exhaust valve (15), - actuating means (16) of the exhaust valve ( 15) for successively opening and then closing the exhaust valve at predetermined moments of the engine cycle, - control means (17) of the actuating means (16) of the exhaust valve (15) depending on the fuel used by the engine, characterized in that the actuating means (16) of the exhaust valve (15) are designed to successively open and then close the exhaust valve (15) during a part of the compression phase in order to to let some of the gases escape are contained in the cylinder by the exhaust pipe, so as to obtain an effective compression ratio adapted to the fuel used by the engine.

Description

Internal combustion engine of the poly-fuel type with direct injection with spark ignition. TECHNICAL FIELD OF THE INVENTION The present invention relates to the field of internal combustion engines and more particularly to the control of spark ignition engines that can operate with different fuel mixtures. New engines must respond to a problem that is becoming more and more restrictive, in particular to increasingly stringent regulatory limits on pollutant emissions and CO2 emissions. For this purpose, some vehicles are equipped with poly-fuel engines spark ignition, commonly referred to in the automotive field by the English expression "flex-fuel". These "flex-fuel" polyfuel engines are engines designed to use a first fuel, for example gasoline, a second fuel, for example ethanol, or a mixture between the first fuel and the second fuel in variable proportions from one fill to another of the tank of the vehicle.

However, depending on the proportion between the first fuel and the second fuel in the tank, the engine needs adjustment adapted to optimize combustion. An important tuning parameter is the compression ratio of the motor. On spark ignition engines, a high compression ratio favors the combustion efficiency and the increase in power, as well as the risk of knocking. The knock resistance is also dependent on the fuel. The adequate compression ratio is therefore variable according to the proportions of the mixture between the first fuel and the second fuel intended to be injected into the combustion chamber.

Document FR2927655 discloses a variable dispensing device for a poly-fuel type indirect injection controlled ignition engine adapted for controlling at least the openings and closures of the engine intake valves as a function of the proportions of the mixture between a first fuel and a second fuel. The compression ratio can be controlled by the intake valve, by acting on the valve crossover so as to simulate an internal EGR, in which case the exhaust gases return to the cylinder, which penalizes the air filling. and therefore the available torque. Document US20100024750 is still known which proposes on an internal combustion engine with indirect injection to reduce the compression ratio by letting escape during the compression phase a part of the fluid present in the cylinder towards the inlet. However, the return of air through the intake generates turbulence in the intake and the temperature of the intake air can increase due to air from the cylinder, with a penalizing effect on the filling.

Therefore, the problem underlying the invention is to overcome the aforementioned drawbacks and to provide a device that provides an adequate compression rate for use in the same engine of different fuels, without penalizing the filling of air admitted.

To achieve this objective, it is provided according to the invention an internal combustion engine of the poly-fuel direct injection type with controlled ignition operating on a motor cycle comprising a compression phase and comprising: - a cylinder, - a pipe of exhaust of combustion gases produced in the cylinder of the engine in communication with this cylinder by means of an exhaust valve, - means for actuating the exhaust valve for successively opening and closing the exhaust valve at determined moments of the engine cycle, means for controlling the means for actuating the exhaust valve as a function of the fuel used by the engine, characterized in that the means for actuating the exhaust valve are designed to successively open and then close the exhaust valve during a part of the compression phase in order to let part of the gases present in the cylinder escape by the exhaust pipe, so as to obtain an effective compression ratio adapted to the fuel used by the engine. In the invention, the effective compression ratio can therefore be adjusted to the fuel used by the engine. In addition, the exhaust valve remains open during the beginning of the compression phase. In this situation, only air admitted by the intake valve is expelled through the exhaust valve.

Preferably, the engine cycle also comprising an exhaust phase, the means for actuating the exhaust valve comprise a first profile defining a law for lifting the exhaust valve during the exhaust phase and a second profile defining a law of emergence of the exhaust valve (15) during the portion of the compression phase. In a variant, the means for actuating the exhaust valve comprise means for angularly shifting the second profile, the control means being adapted to control the angular offset of the second profile as a function of the fuel used by the engine. In a variant, the means for actuating the exhaust valve comprise a one-piece cam, the first and second profiles being integral with this cam.

In another variant, the actuating means of the exhaust valve comprise a cam whose second profile can have a variable angular offset independently of the first profile.

In another variant, the means for actuating the exhaust valve are designed to optimize the effective compression ratio to one of the fuels used by the engine. In another variant, the actuating means are designed to open and then close the exhaust valve only during part of the compression phase. In another variant, the motor comprises a linear or proportional wealth sensor disposed in the exhaust pipe.

The invention also relates to a motor vehicle comprising an engine according to any one of the previously described variants. The invention also relates to a method of operation of a direct-injection direct injection poly-fuel type internal combustion engine operating on an engine cycle comprising a compression phase, the engine comprising a cylinder, an exhaust pipe combustion gases produced in the cylinder of the engine in communication with this cylinder by means of an exhaust valve, the method comprising a step of detecting the fuel used by the engine, and characterized by a step of opening and then of closing the exhaust valve during a portion of the compression phase to allow a portion of the gases present in the cylinder to escape through the exhaust pipe, so as to obtain an effective compression ratio adapted to the fuel used by the engine . BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages will appear on reading the following description of a particular embodiment, not limiting of the invention, with reference to the figures in which: - Figure 1 is a representation schematic of a vehicle equipped with a direct injection internal combustion engine with direct injection type polyfuels of the invention. FIG. 2 shows on a Pressure-Volume diagram, a simplified simulation of a four-phase operating cycle of a spark ignition direct injection engine according to the prior art. FIG. 3 shows on a Pressure-Volume diagram a simplified simulation of a four-phase operating cycle of an engine of the invention according to a first embodiment for a first fuel. - Figure 4 shows in section in cross section a double profile cam provided for the first embodiment of the motor of the invention. FIG. 5 shows on a Pressure-Volume diagram a simplified simulation of a four-phase operating cycle of an engine of the invention according to the same embodiment as that mentioned in FIG. 3 for a second fuel. FIG. 6 shows on a Pressure-Volume diagram a simplified simulation of a four-phase operating cycle of an engine of the invention for a second embodiment and for the second fuel. FIG. 7 shows on a pressure-volume diagram a simplified simulation of a four-phase operating cycle of an engine of the invention for a third embodiment and for the second fuel.

DETAILED DESCRIPTION FIG. 1 schematically represents a vehicle 1 equipped with an internal combustion engine. For example, the vehicle 1 is a motor vehicle such as a car.

The engine of the vehicle 1 is equipped with several cylinders. However, to simplify the illustration, only a cylinder 2 of this combustion engine is shown in Figure 1. Inside the cylinder 2, a piston 3 is mounted movable in translation between a top dead center (TDC) and a bottom dead center (PMB). This piston 3 rotates a crank 4 of a crankshaft 5 by means of a connecting rod 6. The crankshaft 5 drives in rotation, through a mechanism (not shown), the drive wheels of the vehicle 2 such that the wheel 7.

The cylinder 2 defines a combustion chamber 8 delimited by the upper part of the piston 3 and a cylinder head not shown. A duct 9 fresh air intake opens into the chamber 8 via an inlet opening. An intake valve is movable between a closed position in which it closes the intake opening in a fresh airtight manner, and an open position in which fresh air can be admitted into the interior of the chamber. room 8 through the intake opening. The valve 10 is moved between its open position and its closed position by actuating means 11 of the intake valve. A fuel injector 12 is provided in the cylinder 2 to inject the fuel directly inside the chamber 8. A spark plug 13 placed in the cylinder 2 and able to ignite the fresh air / fuel mixture in the combustion chamber 8 is also planned. An exhaust duct 14 also opens into the combustion chamber 8 via an exhaust opening. This exhaust opening is closable by an exhaust valve movable between a closed position and an open position in which the burnt gases contained inside the chamber 8 can escape via the conduit 14. This valve 15 is moved between these open and closed positions by actuating means 16, embodiments of which will be detailed later. The various equipment of the engine that can be controlled such as the actuators 11, 16, the spark plug 13 or the fuel injector 12 are connected to means 17 for controlling the engine or computer designed to control them, in particular depending on the fuel used by the engine which is said to be fuels because planned to use more fuels. The engine can be provided to use a first fuel for example gasoline, a second fuel, for example ethanol, or a mixture between the first fuel and the second fuel in varying proportions from one filling to another of the vehicle tank. To simplify FIG. 1, the connections between this unit 17 and the various equipment items ordered have not been represented.

The computer 17 is also connected to a wealth sensor 18 implanted in the exhaust duct 14. The computer 17 can also be connected to many other sensors such as for example a sensor 19 of the engine speed N. Due to the operation of the invention will be detailed later, even when the engine operates in a stoichiometric condition, the exhaust duct 14 is crossed by gases whose richness is poor view by the wealth probe 18. This must be linear or proportional to distinguish the different levels of wealth of the exhaust gas through the exhaust duct 14.

The computer 17 comprises means for detecting the fuel used by the engine as a function of the richness of the exhaust gases detected by the richness sensor 18. The computer 17 also comprises means for controlling the valve actuator 16. exhaust 15 depending on the fuel detected.

FIG. 2 shows on a pressure-volume diagram a simplified simulation of a four-phase operating cycle of a direct injection engine according to the prior art, with a fixed geometric compression ratio of 14.5. The geometric compression ratio, tcg, is defined by the known relation: = VpmH VPMB being the volume of the cylinder when the piston is at Low Dead Point (PMB) and and VPMH the volume of the cylinder when the piston is at Top Dead Center ( TDC). During this cycle, the phase of admission of air into the cylinder instead of point A for which the piston is at Top Dead Point (TDC) at point BA for which the piston is at Low Dead Point (PMB) . During this intake phase, the intake valve is open and the exhaust valve is closed. After the intake phase comes the compression phase (from point B to point C), during which the intake valve and the exhaust valve are closed, the piston moves from the lowest dead point (PMB) to Top Dead Point (TDC). In the case of a direct injection engine, the fuel is injected and then the air / fuel mixture is ignited during this phase of VPMB compression, at the point In and then at the point Ig. After the compression phase comes the expansion phase (from point C to point E), during which the intake valve and the exhaust valve are closed, the piston moves again from the Top Dead Center (TDC) to the dead point Low (PMB). After the expansion phase comes the exhaust phase (from point E to point A) during which the intake valve is closed, the exhaust valve is opened, the piston moves from the bottom dead point (PMB) to the point Death High (PMH). FIG. 3 now shows on a pressure-volume diagram a simplified simulation of a four-phase operating cycle of a direct injection engine according to a first embodiment of the engine of the invention. The geometric compression ratio is still 14.5. The operating cycle of FIG. 3 differs from that of FIG. 2 in that at the beginning of the compression phase the exhaust valve opens at the point BO, which in this example coincides with the point B at the beginning of compression. and closes during the compression phase at point B1, before the injection of the fuel, at the point In. In this case the pressure increase of the gases in the cylinders actually starts from the point B1, which allows to adjust the effective compression ratio to a value lower than that of the geometrical compression ratio by allowing part of the gases present in the cylinder to escape during part of the compression phase through the exhaust pipe 14. case the effective compression ratio is optimized for a first fuel E100 (100% ethanol) is here 13.5.

The effective compression ratio, tc eff, taking into account the actual volume VB1, compressed by the piston between its position at the closing of the exhaust valve at point B1 and the PMH, during the compression phase of the engine cycle is then defined by the following relationship: VB1 VPMH To achieve the operating cycle of Figure 3, it is intended to use for this first embodiment of the actuating means 16 comprising a double profile cam as shown in FIG. 4. The two profiles are integral with the cam which is monobloc. In FIG. 4 is shown in cross section such a cam 20. This cam 20 comprises a first profile 21 defining the law of emergence of the exhaust valve during the exhaust phase and a second profile 22 defining a law during the compression phase, between BO and B1 in FIG. 3. The cam 20 can be carried by a camshaft 23. In order to adapt the effective compression ratio to a second fuel, for example the E22 (Gasoline comprising 22% ethanol), the actuating means may comprise angular setting means of the cam 20 relative to the crankshaft of the engine. In this first embodiment, the cam 20 is angularly offset as a whole. The computer 17 is then adapted to control the angular offset of the second profile 22 as a function of the fuel used by the engine. FIG. 5 shows on a pressure-volume diagram a simplified simulation of a four-phase operating cycle of a direct injection engine according to the first embodiment of the invention. The operating cycle of FIG. 5 differs from that of FIG. 3 in that the exhaust valve opens later during the compression phase (the point BO is not coincident with the point B) a part of the compression phase. Therefore the exhaust valve closes during the compression phase at point B1 also later than in Figure 3, before the fuel injection. In this case, the pressure increase of the gases in the cylinder actually starts from the point B1, which makes it possible to adjust the effective compression ratio to a value lower than that of the geometric compression ratio, having lost part of the compression phase a portion of the gas present in the cylinder through the exhaust pipe 14. In this case the effective compression ratio is adjusted to 10.5 for the operation of the engine with a second fuel, by example of E22 (22% ethanol). This offset is obtained by an angular offset of the cam 20 as a whole relative to the crankshaft so that the second profile 22 defining a law of emergence of the exhaust valve during the compression phase, between BO and B1 operates later during the compression phase with the first fuel requiring a higher effective compression ratio. In this first embodiment, the actuating means 16 of the exhaust valve 15, in particular the cam 20 and its angular offset in the compression phase are designed to optimize the effective compression ratio at least one of the fuels used by the engine, here the E100. For other fuel used by the engine such as the E22 we can adjust the effective compression ratio, here 10.5, but without reaching an optimum would be rather a compression ratio of 9. The E100 is chosen as a reference fuel here because its optimum compression ratio is the closest to the geometric compression ratio of the engine.

In a second embodiment, it can be provided that the actuating means 16 comprise a cam whose second profile 22 can have a variable angular offset independently of the first profile 21, for example by an appropriate three-dimensional shape or concentric profiles.

In this second embodiment, the actuating means 16 of the exhaust valve 15, in particular the cam 20 and its angular offset in the compression phase, are designed to optimize the effective compression ratio at least one of the fuels used. by the engine, here the E100. The operating cycle of this second embodiment, for the first fuel E100, illustrated on a Pressure-Volume diagram, corresponds to that shown in Figure 3 for the first embodiment with this fuel. FIG. 6 shows on a pressure-volume diagram a simplified simulation of a four-phase operating cycle of a direct injection engine according to a second embodiment, with the second fuel E22. The operating cycle of FIG. 6 shows, as for FIG. 5, that the exhaust valve opens and closes later during the compression phase (point BO is not coincident with point B), only in FIG. 3. In this case, the pressure increase of the gases in the cylinder actually starts from the point B1, which makes it possible to adjust the effective compression ratio to a value lower than that of the geometric compression ratio. having escaped during part of the compression phase a portion of the gases present in the cylinder through the exhaust pipe 14. In this case the effective compression ratio is adjusted to 10.5 for the operation of the engine with a second fuel, for example E22 (22% ethanol). This offset is obtained by an angular offset of the second profile 22 of the cam 20 relative to the crankshaft.

However, unlike FIG. 5, the first profile 21 having not been angularly offset in this second embodiment, the Pressure-Volume diagram does not show the part in H (between E and B) visible in FIG. 5, due to the angular displacement of the first profile 21 integrally with the second profile 22. The work cycle is better in this second embodiment. In a third embodiment it can further be provided that the actuating means 16 are designed to open and then close the exhaust valve 15 only during part of the compression phase. The exhaust valve 15 is then dedicated to this opening during the compression phase. Another exhaust valve is then provided for opening during the exhaust phase of the engine cycle.

In this third embodiment, the operating cycle for the first fuel E100, illustrated on a pressure-volume diagram, corresponds to that shown in FIG. 3 for the first embodiment with this same fuel.

FIG. 7 shows on a pressure-volume diagram a simplified simulation of a four-phase operating cycle of a direct injection engine according to this third embodiment, with the second fuel E22. The operating cycle of FIG. 7 shows that the exhaust valve closes again later during the compression phase than in FIG. 3. In this case, the pressure increase of the gases in the cylinder actually starts from the point B1, which makes it possible to adjust the effective compression ratio to a value lower than that of the geometric compression ratio having, during a part of the compression phase, allowed part of the gases present in the cylinder to escape through the exhaust pipe 14. In this case the effective compression ratio is adjusted to 10.5 for the operation of the engine with a second fuel, for example E22 (22% ethanol). The advantages of this third variant is to allow an adjustment of the duration and the lifting of the exhaust valve. Since the pressure in the cylinder at the beginning of compression is low, the opening of the valve at this moment requires little effort and therefore allows less restrictive sizing compared to an exhaust valve that must open during the exhaust phase. From an operating point of view, the main stages in the operation of the engine of the invention are the following: detection of the fuel used by the engine, for example by means of the richness probe 18 and control means 17, opening and closing of the exhaust valve 15, by means of the control means 17 and actuation 16 of the exhaust valve 15, during part of the compression phase in order to let out some of the gases present in the cylinder 2 by the exhaust pipe 14, so as to obtain an effective compression ratio adapted to the fuel used by the engine. Comparison of the advantages of the three embodiments: The first mode is the least expensive, but one loses efficiency when one reduces the effective compression ratio. The second mode is higher cost in the first embodiment but less efficiency is lost when reducing the effective compression ratio.

The third mode is higher cost in the second embodiment, but as the opening to the exhaust during the exhaust phase is independent of that during the compression phase, we do not lose efficiency.

The invention allows a wide variation in the effective compression ratio, which allows an adaptation of the operation of the same engine with several fuels. The invention makes it possible to avoid rattling phenomena without reducing the ignition advance, thus without degrading the combustion, which makes it possible to maintain the performance and the pleasure of the engine, particularly its torque.

Claims (10)

REVENDICATIONS1. A direct injection direct injection poly fuel type internal combustion engine operating on an engine cycle comprising a compression stage and comprising: - a cylinder (2), - an exhaust pipe (14) for the combustion gases produced in the cylinder (2) of the engine in communication with this cylinder (2) by means of an exhaust valve (15), - actuating means (16) of the exhaust valve (15) for successively opening and closing the exhaust valve at specified times (BO, B1) of the engine cycle, - control means (17) of the actuating means (16) of the exhaust valve (15) depending on the fuel used by the engine, characterized in that the actuating means (16) of the exhaust valve (15) are adapted to successively open and close the exhaust valve (15) during a part of the compression phase in order to let some of the gases present in the cylinder through the exhaust pipe, so as to obtain an effective compression ratio adapted to the fuel used by the engine. 2. Engine according to claim 1, characterized in that the engine cycle also comprising an exhaust phase, the actuating means (16) of the exhaust valve (15) comprise a first profile (21) defining a law of emergence of the exhaust valve (15) during the exhaust phase and a second profile (22) defining a law of emergence of the exhaust valve (15) during the portion of the compression phase. 25 3. Motor according to claim 1 or claim 2, characterized in that the actuating means (16) of the exhaust valve (15) comprise angular displacement means of the second profile (22), the moyeris commands (17) being adapted to control the angular offset of the second profile (22) depending on the fuel used by the engine. 30 4. Engine according to any one of claims 1 to 3, characterized in that the actuating means (16) of the exhaust valve (15) comprise a cam (20) monobloc, the first and the second profile ( 21, 22) being integral with this cam (20). 5. Motor according to claim 3, characterized in that the actuating means (16) of the exhaust valve (15) comprise a cam (20) whose second profile (22) can have a variable angular offset independently of the first profile (21). 6. Engine according to any one of the preceding claims, characterized in that the actuating means (16) of the exhaust valve (15) are designed to optimize the effective compression ratio to one of the fuels used by the engine. An engine according to claim 1, characterized in that the actuating means (16) is adapted to open and then close the dispensing valve (15) only during part of the compression phase. 8. Motor according to any one of the preceding claims, characterized in that it comprises a linear or proportional wealth sensor (18) disposed in the exhaust pipe (14). 9. Motor vehicle, characterized in that it comprises an engine according to any one of the preceding claims. 10. A method of operating an internal combustion engine of the polyurethane direct injection type with positive ignition operating on an engine cycle comprising a compression phase, the engine comprising a cylinder (2), an exhaust pipe (14). ) combustion gases produced in the cylinder (2) of the engine in communication with the cylinder (2) by means of an exhaust valve (15), the method comprising a step of detecting the fuel used by the engine, and characterized by a step of opening and closing the exhaust valve (15) during a portion of the compression phase to allow a portion of the gases present in the cylinder (2) to escape through the exhaust pipe ( 14), so as to obtain an effective compression ratio adapted to the fuel used by the engine.