Method for controlling a stratified combustion internal combustion engine for knock noise reduction and corresponding powertrain

Abstract

Method for controlling an internal combustion engine, comprising cylinders designed to allow stratified combustion to be carried out, comprising the following steps, for each combustion cycle: determining (31) the number of injection and combustion patterns to be carried out, determining (32) the quantity of fuel to be injected at each injection by dividing the quantity of fuel to be injected in the combustion cycle divided by the number of patterns to be carried out, determining (33) the time of each pattern as a function of the crankshaft angle, said time of each pattern being between the bottom dead center of intake and the top dead center of combustion of the combustion cycle, controlling (34) the fuel injection circuit and the ignition means in order to carry out the patterns as a function of the crankshaft angle, the quantity of fuel to be injected per pattern and the time of each pattern. Figure for abstract: Fig 4

Description

Title of the invention: Method for controlling a stratified combustion internal combustion engine for reducing knocking noise and corresponding powertrain Technical field

[0001] The technical field of the invention is direct injection spark ignition internal combustion engines. Previous techniques

[0002] Figure [Fig.l] illustrates an internal combustion and spark ignition engine 1 comprising at least three cylinders 2 connected by a distributor, or intake manifold 3 to an intake circuit and by an exhaust manifold 4 to an exhaust circuit. In this example, it is an engine supercharged by a turbocharger.

[0003] Each cylinder 2 is provided with a fuel injector connected to a fuel supply circuit, intake valves opening into the distributor, or intake manifold and exhaust valves opening into the exhaust manifold. Each cylinder 2 is also provided with a piston for compressing the air / fuel mixture before ignition, and for transmitting the momentum generated by the ignition to a crankshaft of the engine. A spark plug is also provided for igniting the air / fuel mixture.

[0004] The intake circuit comprises a fresh air intake 5, generally provided with an air filter 5a, connected to the inlet of a compressor 6a of a turbocharger 6. The outlet of the compressor 6a is connected to an intake valve 7, in particular of the throttle body type, itself connected to the distributor 3. A charge air cooler 8 is arranged between the compressor and the intake valve.

[0005] The exhaust manifold is connected to the inlet of a turbine 6b of the turbocharger 6, the outlet of the turbine 6b being connected to an air vent 9 via a pollution control system 10 comprising in particular a particulate filter and a three-way catalyst.

[0006] The state of the art consists of the ignition of a homogeneous air / fuel mixture as a function of the crankshaft angle. The fuel injection, of the direct injection type, is done directly into the combustion chamber, defined by the volume of the cylinder delimited by the piston and into which the fuel injector, the valves and the ignition means open. The injection takes place at the start of the cycle before the bottom dead center of the intake PMB.

[0007] The quantity of fuel injected is controlled by an engine computer internal combustion to ensure an air / fuel mixture at stoichiometry (i.e. richness equal to 1). This injection takes place for example quite early in the cycle, during the intake stroke of the 4-stroke cycle, before the Bottom Dead Center (BDC) of intake. The mixture then obtained is very homogeneous at the time of ignition which takes place towards the end of the compression stroke. For example, the moment of ignition takes place at 20°Vil before the Top Dead Center (TDC) of combustion. This ignition is carried out by the spark plug which is also controlled by the engine computer via an ignition coil.

[0008] Although very efficient, this type of control presents a combustion phenomenon known as "knock" well known on spark-ignition engines. Knock appears from a certain level of engine load when the pressure and temperature conditions in the cylinder are high. This typically occurs when the pressure in the distributor, or intake manifold Pcol exceeds an absolute value of 1 bar, which occurs at certain operating points of a supercharged engine. This abnormal phenomenon is a self-ignition of the mixture after ignition at several locations in the combustion chamber before the flame front has burned the fuel by so-called diffusion combustion, which is the normal combustion mode on spark-ignition engines. This phenomenon can be observed on a graph illustrating the pressure in the cylinder Pcyl as a function of the crankshaft angle °Vil.We then observe strong pressure oscillations superimposed on the expected variation in pressure during the cycle. Figure [Fig.3] illustrates such a curve in dashed lines and bearing the reference 20. This phenomenon leads in particular to the generation of noise, called clicking noise, with a "metallic" sound and perceptible to the customer. Clicking is also the source of degradation or even destruction of the piston.

[0009] It is then necessary to reduce the ignition advance to counter this phenomenon, which degrades the engine's efficiency (higher fuel consumption) and limits maximum performance.

[0010] With the advent of high-efficiency engines operating according to the so-called "Miller" or "Atkinson" cycles, the knocking problem is even more present at high and full load. This is due to the fact that these processes use high levels of Volumetric Compression Ratio (VCR between 12 and 14 compared to around 10 usually), which are very unfavorable for knocking. Indeed, these high levels increase the pressure and temperature in the combustion chamber. The efficiency gain linked to the increased VCR is therefore reduced by the need to reduce the ignition advance to counter the knocking in the critical zone. We therefore do not benefit from the full efficiency gain associated with these processes. Fuel consumption is therefore not optimal, and the same is true for carbon dioxide CO2 emissions, which are also increasingly constrained by regulations.

[0011] There is therefore a need for a reduction in knocking in combustion engines. internal and spark ignition.

[0012] From the state of the prior art, document EP1770256B1 is known, disclosing a method for operating a stratified mixture engine in which the fuel injection is carried out in two successive distinct sequences, during the compression stroke, before ignition.

[0013] Document DE102004017988A1 is also known, disclosing a method for operating a stratified mixture engine in which the injection comprises a first injection sequence carried out during the intake stroke, then a second main injection sequence carried out during the compression stroke.

[0014] It is expected that the main injection sequence can be divided into several consecutive phases (2 or 3).

[0015] Ignition is carried out near the top dead center at the end of compression.

[0016] When there are two injection phases, ignition can occur after the two phases or between the first phase and the second phase.

[0017] When there are three phases, ignition can occur after the three, or between the first phase and the second phase, or between the second phase and the third phase.

[0018] In these documents, only one ignition is provided.

[0019] The technical problem remains unchanged. Statement of the invention

[0020] The subject of the invention is a method for controlling an internal combustion engine, comprising cylinders and pistons designed to allow stratified combustion to be carried out, comprising the following steps, for each combustion cycle:

[0021] a. determining the number of injection and combustion patterns to be carried out in the combustion cycle,

[0022] b. determining the quantity of fuel to be injected at each injection prior to an injection and combustion pattern by dividing the quantity of fuel to be injected in the combustion cycle divided by the number of injection and combustion patterns to be carried out in the combustion cycle,

[0023] c. determining the time of each injection and combustion pattern as a function of the crankshaft angle, said time of each injection and combustion pattern being between the bottom dead center of intake and the top dead center of combustion of the combustion cycle,

[0024] d. controlling the fuel injection circuit and the ignition means in order to carry out the injection and combustion patterns as a function of the crankshaft angle, the quantity of fuel to be injected per injection and combustion pattern and the time of each injection and combustion pattern.

[0025] Before the step of determining the number of injection and combustion patterns to be carried out in the combustion cycle, the following steps can be carried out:

[0026] a. determining the presence of the operating point in a knocking zone as a function of a predetermined map accepting as input the load and the rotation speed of the internal combustion engine,

[0027] b. if the operating point is in a knocking zone, controlling the internal combustion engine in injection and combustion pattern and continuing the method by the step of determining the number of injection and combustion patterns to be carried out per combustion cycle, the number of injection patterns being at least equal to two, each injection taking place during the compression stroke of the engine cycle and being followed by ignition.

[0028] The number of injection and combustion patterns in a combustion cycle may depend on the rotational speed and load of the internal combustion engine.

[0029] The invention also relates to a powertrain for a motor vehicle, comprising an internal combustion engine provided with cylinders designed for stratified combustion, a rotation speed sensor, a control coil for each ignition means, a fuel pump, a fuel injector actuator and an electronic control unit of the internal combustion engine designed to carry out the steps of the control method as described above.

[0030] A fuel injector may be positioned laterally in the combustion chamber.

[0031] An ignition means may be centrally positioned in the combustion chamber.

[0032] Each piston head may have a suitable profile, in the shape of a bowl with a concavity facing the fuel injector and the ignition means, each piston head making it possible to create a rotary movement perpendicular to the axis of the cylinder.

[0033] The control method described above does not present any significant additional cost compared to a control method according to the state of the art and makes it possible to reduce or even eliminate knocking in critical areas. It makes it possible to dispense with reducing the ignition advances which degrade the efficiency and performance of the engine. Fuel consumption and CO2 emissions are reduced. Brief description of the drawings

[0034] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example and made with reference to the appended drawings in which:

[0035] - Figure [Fig.l] illustrates the main elements of an internal combustion engine with supercharging,

[0036] - Figure [Fig.2] illustrates the main elements of a combustion chamber suitable for achieving stratified combustion,

[0037] - figure [Fig.3] illustrates the evolution of the pressure in the cylinder as a function of the crankshaft angle for an engine controlled according to the state of the art and for an engine controlled according to the invention, and

[0038] - figure [Fig.4] illustrates the main steps of a method of controlling a stratified combustion internal combustion engine. Detailed description

[0039] Recent engine control systems are increasingly sophisticated and allow the use of multi-injection strategies (several injections per cycle instead of just one, typically up to 5) and multi-spark strategies (several ignitions per cycle instead of just one, typically up to 5).

[0040] To reduce or even eliminate knocking in the critical speed / load zone, a so-called "multi-stratified" injection / ignition scheme is used, involving the performance of several injections and ignitions per combustion cycle depending on the crankshaft angle.

[0041] To avoid the knocking phenomenon, the fuel is injected progressively in the form of several injections during the compression time of the cycle, each followed by an ignition. Since the injection is divided, a smaller quantity of fuel is injected each time than that necessary to have a mixture with an average richness of 1. There are at least two injections. For example, if the injection is divided into 3, the first injection has an average richness of approximately 0.33 which cannot burn because the air-fuel mixture, although homogeneous, is too lean.

[0042] It is therefore necessary to use a combustion chamber architecture that allows such “stratified” combustion to be achieved, i.e. in which the richness of the air-fuel mixture is not homogeneous.

[0043] Figure [Fig.2] illustrates a cylinder 2 comprising a cylinder head 11 and a piston 12 together delimiting the combustion chamber 13. At least one intake valve 16, an ignition means 15, at least one exhaust valve 14 and a fuel injector 17 arranged in the cylinder head 11 are also illustrated. The combustion chamber has the specific feature that the fuel is injected as close as possible to the spark plug via the interaction between the fuel jet (referenced 18), the shape of the piston head 12 and the internal aerodynamics.

[0044] More precisely, the piston head has a suitable profile, in the shape of a bowl with a concavity facing the fuel injector 17 (in a lateral position in the combustion chamber) and the ignition means 15 (in a central position in the combustion chamber).

[0045] Internal aerodynamics involves the creation of a rotary movement, called a “tumble”, perpendicular to the axis of the cylinder, due to the shape of the piston head.

[0046] This combustion chamber architecture makes it possible to locally obtain a mixture with a richness substantially equal to 1, which can burn upon ignition by the spark, while the richness over the entire combustion chamber is less than 1.

[0047] Other engines adapted to this type of combustion are known from the state of the art; reference may in particular be made to the devices disclosed in documents EP1429010A1 or EP1770256B1

[0048] The curve showing the evolution of the pressure in the cylinder Pcyl as a function of the crankshaft angle °Vil in a cylinder of an internal combustion engine controlled by the method according to the invention is illustrated in solid lines in the figure [Fig.3] and bears the reference 21. The curve shown no longer shows oscillations, associated with the presence of knocking, unlike the same curve for an internal combustion engine with homogeneous combustion (in dashed lines and bearing the reference 20). This combustion in stages allows a progressive increase in pressure in the cylinder avoiding any knocking phenomenon. The number of “injection + ignition” patterns can be optimized as a function of the rotation speed (also called rpm) and the engine load. Outside the knocking zone, a conventional injection / ignition strategy called “homogeneous” can be maintained.In addition to the pressure criteria defined above, the knock zone is defined as a high load zone, namely from 50% of full load for a given rotational speed. Alternatively, this rate may vary depending on the rotational speed, being greater for low rotational speeds and less important for high rotational speeds.

[0049] Figure [Fig.4] illustrates the method of controlling an internal combustion engine equipped with combustion chambers designed for stratified combustion. For each combustion cycle, the following steps are carried out:

[0050] During a first step 31, the number of injection and combustion patterns to be carried out per combustion cycle is determined. The number of injection and combustion patterns is in particular predetermined and stored.

[0051] During a second step 32, the quantity of fuel to be injected at each injection prior to an injection and combustion pattern is determined by dividing the quantity of fuel to be injected per combustion cycle divided by the number of injection and combustion patterns to be carried out per combustion cycle.

[0052] During a third step 33, the time of each injection and combustion pattern is determined as a function of the crankshaft angle °Vil. The time of each injection and combustion pattern being between the intake PMB and TDC combustion.

[0053] During a fourth step 34, the fuel injection circuit and the ignition means are controlled in order to produce the injection and combustion patterns as a function of the crankshaft angle °Vil, the quantity of fuel to be injected per injection and combustion pattern and the time of each injection and combustion pattern.

[0054] In a particular embodiment, the control method comprises a preliminary step 30, during which it is determined whether one is in the knocking zone by comparing the load and the rotation speed with a predetermined map.

[0055] If one is not in a knocking zone, the internal combustion engine is controlled in homogeneous combustion.

[0056] If a knocking zone is found, the internal combustion engine is controlled in stratified combustion, and the control method continues with the first step 31.

Claims

Claims

1. A method of controlling a spark-ignition internal combustion engine, comprising cylinders and pistons designed to enable stratified combustion to be achieved, comprising the following steps, for each combustion cycle: a. determination (31) of the number of injection and combustion patterns to be carried out in the combustion cycle, b. determining (32) the quantity of fuel to be injected at each injection prior to an injection and combustion pattern by dividing the quantity of fuel to be injected in the combustion cycle divided by the number of injection and combustion patterns to be carried out in the combustion cycle, c. determining (33) the time of each injection and combustion pattern as a function of the crankshaft angle, said time of each injection and combustion pattern being between the bottom dead center of intake and the top dead center of combustion of the combustion cycle, d. control (34) of the fuel injection circuit and the ignition means in order to carry out the injection and combustion patterns as a function of the crankshaft angle, the quantity of fuel to be injected per injection and combustion pattern and the time of each injection and combustion pattern.

2. Control method according to claim 1, in which, before the step of determining the number of injection and combustion patterns to be carried out in the combustion cycle, the following steps are carried out: a. determination of the presence of the operating point in a knocking zone based on a predetermined map accepting as input the load and rotation speed of the internal combustion engine, b. if the operating point is in a knocking zone, control of the internal combustion engine in injection and combustion pattern and continuation of the process by the step of determining the number of injection and combustion patterns to be carried out per combustion cycle, the number of injection patterns being at least equal to two, each injection taking place during the compression time of the combustion cycle of the engine and being followed by ignition.

3. A control method according to claim 1 or 2, wherein the number of injection and combustion patterns in a combustion cycle depends on the rotational speed and load of the internal combustion engine.

4. A powertrain for a motor vehicle, comprising an internal combustion engine provided with cylinders designed for stratified combustion, a rotational speed sensor, a control coil for each ignition means, a fuel pump, a fuel injector actuator and an electronic control unit of the internal combustion engine designed to carry out the steps of the control method as claimed in claims 1 to 3.

5. A powertrain according to claim 4, wherein a fuel injector (17) is positioned laterally in the combustion chamber.

6. A powertrain according to claim 4 or 5, wherein an ignition means (15) is centrally positioned in the combustion chamber.

7. A powertrain according to any one of claims 4 to 6, wherein each piston head has a suitable bowl-shaped profile with a concavity facing the fuel injector (17) and the ignition means (15), each piston head allowing a rotary movement to be created perpendicular to the cylinder axis.

Images