Method for controlling an internal combustion engine

Abstract

The invention relates to a method for controlling a four-stroke, spark-ignition internal combustion engine (1) comprising: - at least one cylinder (11), - a fresh air intake line (20) including a compressor (22), - an exhaust line (80) including a catalyst (83) followed by a turbine (82), - an ignition circuit including a spark plug (70) in each cylinder (11), - a fuel injection circuit (60), the control method comprising a step of acquiring an engine control setpoint and a step of primary fuel injection at each intake stroke according to the acquired control setpoint. According to the invention, the method comprises, when said control setpoint requires acceleration: - a step of acquiring engine operating parameters, and - a step of secondary fuel injection at the expansion stroke, after the spark has been generated. Figure for the abstract: Fig. 1

Description

Title of the invention: Method for controlling an internal combustion engine Technical field of the invention

[0001] The present invention relates generally to the reduction of polluting emissions from internal combustion engines.

[0002] It relates more particularly to a four-stroke internal combustion engine known as intake, compression, expansion and exhaust, this engine comprising: - at least one cylinder delimiting a combustion chamber, - a fresh air intake line opening into the combustion chamber and which includes a compressor, - a burnt gas exhaust line outside the combustion chamber which comprises, on the one hand, a turbine adapted to drive the compressor, and, on the other hand, a burnt gas depollution catalyst, located upstream of the turbine, - an ignition circuit which comprises a spark plug opening into each cylinder and which is adapted to generate at least one spark at each compression or expansion stroke, and - a fuel injection circuit into the combustion chamber.

[0003] It also relates to a method for controlling such an internal combustion engine, comprising a step of acquiring an engine control instruction followed by a step of controlling a main injection of fuel into the combustion chamber, at each intake stroke, as a function of the acquired control instruction.

[0004] It also relates to a motor vehicle equipped with such an internal combustion engine. State of the art

[0005] Within an ever more restrictive legislative framework and with a view to preserving the environment, we are currently seeking technical solutions to improve the operation of internal combustion engines, in particular to reduce the level of polluting elements contained in the burnt gases (combustion gases) released by the engines into the atmosphere.

[0006] To reduce these polluting emissions, a turbo-compressed internal combustion engine generally comprises, in its exhaust line, a turbine followed by a combustion gas depollution catalyst, in particular a three-way catalyst in the case of a spark-ignition engine, within which reactions chemicals occur to transform polluting compounds into compounds that have no effect on health.

[0007] Such a catalyst operates optimally when its temperature is above approximately 350°C. However, it exhibits significantly reduced performance at ambient temperature, just after the engine has been cold-started, and in particular below 150°C. Consequently, the majority of pollutants released into the atmosphere are emitted in the minutes following the engine's cold-start phase.

[0008] With the arrival of new standards (notably Euro7), it was decided that this situation should not continue.

[0009] One solution to improve the efficiency of the catalyst would then be to size it according to its performance at low temperatures, by increasing its size. By efficiency, we mean the percentage of polluting compounds of a given species entering the catalyst that it actually transforms into harmless compounds. For example, for a three-way catalyst, we speak of the efficiency of the catalyst in terms of oxidation of carbon monoxide CO or unburned hydrocarbons HC, or the efficiency of the catalyst in terms of reduction of nitrogen oxides NOx.

[0010] Nevertheless, given the high price of the precious materials used to manufacture such a catalyst, it appears difficult to limit the phenomenon of polluting discharges by this means.

[0011] Another solution is described in the document published under the reference FR3122699.

[0012] This solution consists of placing the catalyst upstream of the turbine, as close as possible to the engine exhaust manifold. As a result, the temperature rise rate of the catalyst after the engine is cold started is much faster than in the usual case where the catalyst is placed downstream of the turbine. Indeed, the catalyst can be placed directly in contact with the exhaust manifold, near which it heats up. In addition, the burnt gases leaving the combustion chamber are thus no longer cooled by the turbine before entering the catalyst (the turbine in fact has thermal inertia and causes pressure losses which lead to a drop in the temperature of the burnt gases due to their expansion).

[0013] This solution, however, has the disadvantage that the response time of the turbocharger, particularly during acceleration phases, increases significantly. This response time problem comes from the thermal inertia of the catalyst and the pressure losses generated by this catalyst on the burnt gases. Indeed, the burnt gases which leave the catalyst have limited energy which does not allow them to operate the turbine as quickly as desired.

[0014] So, to reduce this response time, the solution proposed in this document FR3122699 consists of equipping the engine with an air reserve pressurized by a vacuum pump used for a brake booster (or "mastervac"). Thus, during acceleration phases, it is possible to inject pressurized air into the exhaust line, upstream of the catalyst, and increase the richness of the intake air-fuel mixture accordingly. From then on, unburned hydrocarbons and fresh air pass through the catalytic converter, which allows the latter to quickly rise in temperature by exothermic effect and increase the speed of the gases passing through the turbine. In other words, this double injection of air and fuel will make it possible to very quickly increase the enthalpy of the burnt gases passing through this turbine, which will significantly reduce its response time.

[0015] However, this solution requires many components to operate, which makes the vehicle heavier and increases its manufacturing cost. In addition, it is only functional when the air reserve is well pressurized, which is not always the case in practice. Presentation of the invention

[0016] In order to overcome the aforementioned drawbacks of the state of the art, the present invention proposes modifying the sequence (or "pattern") of fuel injection into the combustion chamber in order, during acceleration phases, to very quickly increase the enthalpy of the burnt gases passing through the turbine.

[0017] More particularly, the invention proposes a method for controlling an internal combustion engine as defined in the introduction, in which, when the control instruction requires acceleration of the engine, a step of controlling a secondary injection of fuel into the combustion chamber at the expansion time, after the spark has been generated, is provided.

[0018] Thus, thanks to the invention, this secondary injection of fuel is carried out after the mixture of fuel and fresh air has ignited in the cylinder. Consequently, this surplus fuel is not burned in the cylinders but is discharged into the exhaust line. Unburned hydrocarbons therefore reach the catalyst where they can generate a very exothermic reaction very quickly increasing the enthalpy of the burnt gases which leave this catalyst and pass through the turbine.

[0019] In other words, when the acceleration request exceeds a predetermined threshold and it is therefore desired that the turbine increases in load quickly, it is thus possible to inject fuel and oxygen into the catalyst so that the gases which leave it have a speed favorable to this rapid loading.

[0020] Other advantageous and non-limiting characteristics of the control method according to the invention, taken individually or in all technically possible combinations, are the following: - at least two separate secondary injections of fuel into the combustion chamber are ordered during the said expansion time; - a step of acquiring operating parameters of the internal combustion engine is provided, and said step of controlling at least one secondary injection is implemented only if the operating parameters meet at least one predetermined condition; - said at least one predetermined condition is that a load and / or a speed of the internal combustion engine is within a predetermined range; - said at least one condition is that a temperature relative to the temperature of the catalyst is within a predetermined range; - when the operating parameters meet each predetermined condition, the secondary injection step is implemented at each expansion time, for each cylinder; - the quantity of fuel injected during the main and secondary injection control steps and / or the quantity of fresh air admitted into the combustion chamber is regulated so that the richness of the burnt gases remains substantially equal to 1; - the internal combustion engine comprising a crankshaft, the control step of each secondary injection is implemented when the crankshaft has completed a rotation of between 20° and 60° after the start of the expansion time.

[0021] The invention also proposes an internal combustion engine as defined in the introduction, comprising a computer programmed to implement a control method as mentioned above.

[0022] It also relates to a motor vehicle equipped with such an internal combustion engine.

[0023] Of course, the various features, variants and embodiments of the invention may be combined with each other in various combinations to the extent that they are not incompatible or mutually exclusive. Detailed description of the invention

[0024] The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented.

[0025] In the attached drawings:

[0026] [Fig.l] is a schematic view of an internal combustion engine according to the invention;

[0027] [Fig.2] is a graph illustrating the four operating strokes of the engine at internal combustion of [Fig.l]; and

[0028] [Fig.3] represents several graphs illustrating in a synchronized manner the variations of parameters of the internal combustion engine of [Fig.l], during a transient acceleration phase.

[0029] In the description, the terms “upstream” and “downstream” will be used according to the direction of gas flow, from the point where fresh air is taken from the atmosphere to the outlet of the burnt gases into the atmosphere.

[0030] In [Fig.l], an internal combustion engine 1 fitted to a motor vehicle is schematically represented.

[0031] It could be a hybrid-powered motor vehicle, but here it will be considered to be a purely thermal-powered vehicle.

[0032] The internal combustion engine 1 comprises an engine block 10 provided with a crankshaft and pistons (not shown) respectively housed in cylinders 11 closed on top by a cylinder head. These cylinders, for example four in number, each delimit, with their pistons and the cylinder head, a combustion chamber.

[0033] In the context of the invention, the internal combustion engine is of the spark ignition type (operating for example on gasoline). Consequently, it comprises an ignition circuit which notably comprises spark plugs 70 each opening into a cylinder 11 so as to be able to generate therein an ignition spark of an air-fuel combustion mixture.

[0034] Upstream of the cylinders 11, the internal combustion engine 1 comprises an intake line 20 which takes fresh air from the atmosphere and which opens into an air distributor 25 arranged to distribute the fresh air to each of the cylinders 11 of the engine block 10. This intake line 20 comprises, in the direction of flow of the fresh air, an air filter 21 which filters the fresh air taken from the atmosphere, a compressor 22 which compresses the fresh air filtered by the air filter 21, a main air cooler 23 which cools this compressed fresh air, and an intake valve 24, or throttle body 24, which makes it possible to regulate the flow of fresh air opening into the air distributor 25.

[0035] At the outlet of the cylinders 11, the internal combustion engine 1 comprises an exhaust line 80 which extends from an exhaust manifold 81 into which the gases which have been previously burned in the cylinders 11 discharge, to an exhaust silencer 87 allowing the burnt gases to be expanded before they are discharged into the atmosphere. It also comprises, in the direction of flow of the burnt gases, a catalyst 83 for treating the burnt gases, a turbine 82 and a particulate filter 84.

[0036] The turbine 82 is driven in rotation by the flow of burnt gases leaving the exhaust manifold 81, and it makes it possible to drive the compressor 22 in rotation, thanks to mechanical coupling means such as a transmission shaft. The turbine 82, the compressor 22 and the transmission shaft then form a turbocharger 30.

[0037] The catalyst 83 is located as close as possible to the exhaust manifold 81, and preferably in contact with the latter.

[0038] Since the engine here is of the spark-ignition type, the catalyst 83 is referred to as a “three-way” catalyst in the sense that it is intended to oxidize mainly the unburned hydrocarbons (HC) and carbon monoxide (CO) contained in the burnt gases, as well as to reduce the nitrogen oxides (NOx).

[0039] The internal combustion engine 1 may also include one or more lines for partial recirculation of the burnt gases at the intake (commonly called EGR lines, from the English acronym for: Exhaust Gas Recirculation), originating in the exhaust line 80 and opening into the intake line 20. These lines are not shown here.

[0040] The internal combustion engine 1 further comprises a fuel injection line 60 into the cylinders 11. This injection line 60 comprises an injection pump 62 arranged to take the fuel from a tank 61 in order to bring it under pressure into a distribution rail 63 which opens into the cylinders 11 via fuel injectors 64.

[0041] Thanks to the position of the catalyst 83 upstream of the turbine 82, when the engine is cold started, the temperature of the catalyst increases rapidly, which makes it possible to prime the latter quickly and therefore to ensure as quickly as possible an efficient treatment of the burnt gases. By "priming" is meant the fact that the temperature of the catalyst increases until it reaches a minimum temperature threshold for which its conversion efficiency with respect to the various polluting species reaches a predetermined minimum efficiency threshold. For example, depending on the minimum efficiency value targeted, the minimum temperature threshold is chosen between 150°C and 350°C.

[0042] Because of this position of the catalyst, during acceleration, when the engine moves from a low-load operating point to a high-load operating point, there is a risk that the latency time during which the turbocharger is not effective is prolonged. Indeed, when the catalyst is cold or warm (i.e. primed but at a temperature for example still below 300°C), the burnt gases passing through it are cooled and lose energy, so that they cannot accelerate the turbine 82 as quickly as desired.

[0043] The invention then proposes a solution making it possible to reduce the latency time of the turbine.

[0044] This solution consists of causing rapid heating of the catalyst 83 by bringing unburned hydrocarbons and oxygen into it, via the cylinders 11.

[0045] As shown in [Fig.l], to control the various components of the internal combustion engine 1, a computer 100 is provided comprising a processor (CPU), a random access memory (RAM), a read only memory (ROM), a data input and output interface.

[0046] Thanks to this interface, the computer 100 is adapted to receive input signals from different sensors.

[0047] Among these sensors, there is a lambda probe 85 which is located in the exhaust line 80 and which makes it possible to measure the richness of the burnt gases which circulate in this exhaust line 80. This lambda probe 85 is here located downstream of the turbine 82 but it could alternatively be located upstream of the latter.

[0048] On this subject, it will be recalled that the notion of richness is defined by the ratio between the “effective proportion of fuel in the gases” compared to the “stoichiometric proportion of fuel in the gases”.

[0049] The concept of “proportion of fuel in the gases” corresponds more precisely to the ratio between the mass flow rate of fuel compared to the mass flow rate of air.

[0050] It could be provided that the richness downstream of the catalyst 83 is calculated using a mathematical model, as a function of various exogenous parameters, such as the engine speed, its load, its temperature, etc. Here, as shown in [Fig.l], it will be preferable to use a physical richness probe, for example a proportional type oxygen probe.

[0051] A sensor is also provided for measuring either the pressure exerted by the driver of the vehicle on the accelerator pedal, or the depression of the accelerator pedal.

[0052] In this regard, the notion of depression rate of this pedal will be defined as the ratio between the position of the accelerator pedal and the total travel from which this pedal benefits. This depression rate therefore forms an instruction for controlling the engine, allowing the driver to express his needs in terms of acceleration.

[0053] One or more sensors are also provided for measuring or evaluating the temperature in the catalyst 83.

[0054] A first temperature sensor 86 is provided here, located in the catalyst 83, and a second temperature sensor 88 is located at the inlet of the turbine 82. Alternatively, only one of these two sensors could be used. As a further alternative, the measurements from a set of sensors could be used to evaluate the temperatures in the catalyst 83 and at the inlet of the turbine 82, using a mathematical model.

[0055] Furthermore, a sensor is provided, in a very conventional manner, suitable for measuring the speed of the internal combustion engine, and means for determining the load of this engine.

[0056] Also thanks to its interface, the computer 100 is adapted to transmit output signals to the various components of the engine, in particular to the intake valve 24 and to the injectors 64.

[0057] Thanks to its memory, the computer 100 stores a computer application, consisting of computer programs comprising instructions whose execution by the processor allows the implementation by the computer of the process described below.

[0058] Conventionally, when the engine is started, the fresh air taken from the atmosphere by the intake line 20 is filtered by the air filter 21, compressed by the compressor 22, cooled by the main air cooler 23, then burned in the cylinders 11.

[0059] On leaving the cylinders 11, the burnt gases are treated in the catalyst 83, expanded in the turbine 82, filtered by the particle filter 84 then expanded again in the exhaust silencer 87 before being released into the atmosphere.

[0060] The internal combustion engine 1 operates here on a four-stroke cycle. Thus, as shown in [Fig.2], when each piston slides in a reciprocating motion in its cylinder 11 and drives the rotation of the crankshaft, this engine is arranged in such a way that: - during a first phase of descent of the piston, cylinder 11 admits a mixture of fresh air and fuel, we speak of admission time TA (for the cylinder 11 considered, the crankshaft turns during this time from 0 to 180°), - during a second phase of piston rise, the admitted mixture is compressed and combustion is initiated by ignition, we speak of compression time Tc (the crankshaft rotating during this time from 180 to 360°), - during a third phase of piston descent, the compressed mixture burns and expands in the cylinder, we speak of expansion time TD or explosion (the crankshaft rotating during this time from 360 to 540°), - during a fourth phase of piston rise, the burnt mixture is evacuated from the cylinder, we speak of exhaust time TE (the crankshaft rotating during this time from 540 to 720°).

[0061] The opening of the intake valve (throttle body) 24 and the duration of opening of the injectors 64 at each cycle then make it possible to regulate the speed and load of the engine, in particular as a function of the rate of depression of the accelerator pedal and the speed of the engine.

[0062] To calculate the control instructions for the intake valve 24 and the injectors 64, the computer 100 begins by acquiring the instructions issued by the driver, here in the form of the rate of depression of the accelerator pedal.

[0063] Alternatively, this driving instruction could be issued by a third-party computer, in particular if the vehicle is driven in a partially or fully automated manner.

[0064] The computer also acquires engine operating parameters, which make it possible to define its “operating point”. It will be considered here that this operating point is characterized by the speed of the internal combustion engine 1, by its load and possibly also by the temperature of its catalyst 83.

[0065] Depending on the piloting instruction received and the engine operating point, the cal The controller 100 selects either a standard mode of calculating the control instructions or a particular mode of calculating, which is more specifically the subject of the present invention and occurs during particular acceleration phases. Hereinafter, we will refer to “standard mode” and “particular mode”.

[0066] In the standard mode, the computer 100 is programmed to deduce in particular from the rate of depression of the accelerator pedal a control instruction for the intake valve 24. The idea is that the intake line 20 draws in a sufficient flow of fresh air so that the internal combustion engine can develop the required torque (to move the vehicle forward and meet the other needs of the vehicle - air conditioning, etc.). This deduction is carried out by means of a first map.

[0067] In this standard mode, the computer controls the fuel injectors 64 using a closed control loop according to which: - the value of the intake mixture richness is evaluated using the lambda probe 85, and - the quantity of fuel injected into each cylinder 11 in each cycle is determined so as to regulate the richness value evaluated on a richness setpoint value, here equal to 1.

[0068] In other words, the quantity of fuel injected in each cycle is regulated so that the richness of the burnt mixture remains equal to 1.

[0069] In this standard mode, it is understood that if the internal combustion engine 1 operates at low load and / or low speed, the temperature of the catalyst 83 stabilizes at a reduced temperature.

[0070] Therefore, when the driver accelerates sharply from such an operating point, the thermal inertia of the catalyst 83 will not allow the burnt gases to accelerate the turbine 82 as quickly as desired.

[0071] During such an acceleration phase, it is then provided that the computer 100 controls the intake valve 24 and the fuel injectors 64 in a different manner than in standard mode.

[0072] In practice, the computer first checks whether different conditions are met before exiting standard mode.

[0073] The first condition is that the internal combustion engine 1 accelerates. This condition can for example be verified if the rate of depression of the accelerator pedal increases to a speed greater than a threshold. In the case where the vehicle operates in an automated manner, it can be verified otherwise, for example if the instructions received require a large increase in the engine load.

[0074] The second condition is that the catalyst 83 is cold or warm and that it is likely to slow down the loading of the turbine 82. This second condition is for example verified if the temperature of the catalyst 83 measured by one of the probes of temperature 86, 88 is below a predetermined threshold (e.g. 300°C). It could be checked otherwise, for example if the engine speed has been stabilized at a low value for a period longer than a predetermined time threshold.

[0075] Other conditions may be required (for example that the turbine rotates at a speed below a threshold, and / or that the engine speed is below a threshold, and / or that the engine load is below a threshold...).

[0076] When the required conditions are met, the computer switches to special mode. From then on, it controls the intake valve 24 in such a way that it opens more than in standard mode and the fuel injectors 64 so as to inject fuel after the spark Eb. This control is preferably carried out in such a way that the richness of the burnt gases remains substantially equal to 1.

[0077] As shown in [Fig.2], the idea is indeed to keep a main injection h of fuel to satisfy the torque demand issued by the driver via his accelerator pedal, and to add at least one later secondary fuel injection I2, so that this surplus fuel does not burn in the combustion chamber but in the catalyst 83, with oxygen that has not burned in the combustion chamber. To bring this oxygen to the catalyst, it is therefore also necessary to blow more fresh air into the combustion chamber than in standard mode.

[0078] Thus, as shown in [Fig.2], during each operating cycle, a main injection h of fuel is carried out during the intake stroke TA, and at least one secondary injection I2 of fuel is carried out during the expansion stroke TD. The secondary injection(s) I2 are carried out after the formation of the spark Ei by the spark plug (this spark being generated at the end of the compression stroke Tc or at the start of the expansion stroke TD).

[0079] Thus, the unburned hydrocarbons coming from the secondary injection(s), and the surplus oxygen admitted into the cylinders can then react together within the catalyst 83 in a very exothermic manner, which makes it possible to very quickly increase the temperature of the catalyst 83 and therefore that of the burnt gases passing through the turbine 82. This rapid increase in the temperature of the burnt gases then allows the turbine 82 to quickly increase in speed, which reduces its reaction time.

[0080] Here we can describe more precisely how the control instructions for the intake valve 24 and the fuel injectors 64 are developed.

[0081] Two strategies can then be used.

[0082] The first strategy consists of maintaining the same main injection duration when switching from standard mode to special mode, and carrying out secondary injections of predetermined durations. Thus, the torque demand can continue to be satisfied during this switch. In parallel, the opening of the intake valve 24 can then be regulated so as to maintain a burnt gas richness equal to 1. It is then possible to increase or decrease the main injection duration Ib depending on variations in the rate of depression of the accelerator pedal.

[0083] A second strategy would be to open the intake valve 24 more in special mode than in standard mode, for example by a few degrees. A second mapping could be used in this regard. Then, the duration of the secondary injections I2 being predetermined, the duration of the main injection h could be regulated so as to maintain a richness of the burnt gases equal to 1.

[0084] The objective is to satisfy the torque demand while minimizing the response time of the turbine 82.

[0085] Ideally, as shown in [Fig.2], several secondary injections are carried out, at separate times. At least two secondary injections are planned, but more can be planned, for example four.

[0086] By "distinct" is meant that it is intended to control the stopping and then the resumption of the fuel injection, by allowing a predetermined duration to pass between these two consecutive injections. This duration is at least 250 microseconds.

[0087] These different secondary injections are separated from each other in order to allow time for the fuel to vaporize and mix in the burnt gases. Without this, the rate of fuel in the liquid phase would increase too much, so that this fuel could not vaporize and mix well.

[0088] These secondary injections must not be carried out too early during the expansion time TD, to prevent the fuel thus injected from burning. It must also not be carried out too late to prevent the fuel from wetting the cylinder walls. Indeed, it is preferable for the fuel to be injected towards the piston (when it is high in the cylinder 11) rather than on the wall of the cylinder 11, to prevent it from mixing with the oil contained in the engine. If it were injected too late, when the temperature of the burnt gases has already dropped, it would also not vaporize correctly in the burnt gases and would not mix well with them.

[0089] In practice, these secondary injections are carried out when the crankshaft has an angular position between 380° and 420°, and preferably between 390 and 410°.

[0090] In [Fig.3], the variations of different parameters of the engine are shown during an acceleration phase from a lightly loaded operating point (at low enthalpy), at an instant tb

[0091] Before this instant tb the internal combustion engine 1 was driven in a stabilized manner, with the accelerator pedal lightly depressed (here at a depression rate Eacc equal to 10% of its total travel).

[0092] Since this sinking rate did not increase, the standard mode was selected (the boolean [3 for activating the particular mode was therefore kept equal to zero).

[0093] The temperature T83 of the catalyst 83 was therefore stable and here not very high (of the order of 250°C).

[0094] Similarly, the temperature Tg of the burnt gases remained quite low.

[0095] The engine torque Cm was constant and reduced.

[0096] At time tb the driver suddenly and abruptly presses the accelerator pedal, so that the latter is further depressed (here at a depression rate Eacc equal to 60% of its total travel).

[0097] The above-mentioned conditions then being met (strong acceleration and warm catalyst), the particular mode is selected (the boolean [3 therefore changes to one).

[0098] The intake valve 24 then opens further and the quantity of fuel injected into the cylinders 11 in each cycle also increases, with a main injection h and several secondary injections I2.

[0099] In the three graphs at the top of [Fig.3], the continuous line curves represent the variations that the operating parameters would present in standard mode (without secondary injection). The broken line curves represent the variations that the operating parameters present in special mode, thanks to secondary injections.

[0100] It is first observed that the temperature Tg of the burnt gases between the catalyst 83 and the turbine 82 increases very quickly, due to the aforementioned exothermic reactions. Consequently, the temperature T83 of the catalyst 83 also increases very quickly. The same is true of the torque Cm delivered by the engine, since the turbine accelerates much faster than it would accelerate in standard mode.

[0101] It is then preferentially planned to exit the standard mode at a time t2, namely as soon as one or other of the following three conditions is no longer met.

[0102] The first condition is that the rate of depression of the accelerator pedal and / or the variation of this rate remains(s) greater than a threshold. This condition will for example no longer be met if the driver releases the accelerator pedal.

[0103] The second condition, which will generally be met, is that the temperature T83 of the catalyst 83 does not exceed a predetermined threshold TUm, corresponding to the temperature threshold beyond which it is considered that the catalyst 83 can degrade.

[0104] The third condition will be that the temperature Tg of the burnt gases downstream of the catalyst 83 remains below a threshold. This threshold will be chosen equal to a percentage of the temperature which could be reached in stabilized mode, if the rate of depression of the accelerator pedal no longer varied.

[0105] The idea is to choose this threshold: - high enough for the burnt gases to have reached a sufficient temperature to optimize the loading of turbine 82 before returning to standard mode, and - not too high so as not to significantly increase consumption in engine fuel (the increase in gas temperature being asymptotic, secondary injections further promote this increase when the temperature of the burnt gases is far from the temperature which could be reached in stabilized mode).

[0106] A compromise is therefore made. Here, this compromise consists of choosing a threshold between 85 and 97% of the temperature which could be reached in stabilized mode (typically 95%).

[0107] The present invention is in no way limited to the embodiment described and shown, but those skilled in the art will be able to provide any variant in accordance with the invention.

[0108] Typically, in particular mode, one could plan not to regulate the richness at 1 in closed loop, but to use an intake valve and fuel injection opening map which a priori allows maintaining a burnt gas richness close to 1.

[0109] According to another variant of the invention degraded compared to the mode described above, it could theoretically be provided that in a particular mode, the secondary injections are carried out only in a part of the engine cylinders or intermittently (for example at one operating cycle out of two).

Claims

Claims

1. Method for controlling a four-stroke internal combustion engine (1) with intake (TA), compression (Tc), expansion (TD) and exhaust (TE), said internal combustion engine (1) comprising: - at least one cylinder (11) delimiting a combustion chamber, - an intake line (20) for fresh air opening into the combustion chamber and which comprises a compressor (22), - an exhaust line (80) for burnt gases outside the combustion chamber which comprises, on the one hand, a turbine (82) adapted to rotate the compressor (22), and, on the other hand, a catalyst (83) located upstream of the turbine (82), - an ignition circuit which comprises a spark plug (70) opening into each cylinder (11) and which is adapted to generate at least one spark (EJ) at each compression (Tc) or expansion (TD) stroke, and - an injection circuit (60) of fuel in the combustion chamber,the control method comprising a step of acquiring a control instruction for the internal combustion engine (1) and a step of controlling a main injection (IJ) of fuel into the combustion chamber at each intake time (TA) as a function of the acquired control instruction, characterized in that it further comprises, when the control instruction requires acceleration, a step of controlling at least one secondary injection (I2) of fuel into the combustion chamber at the expansion time (TD), after the spark (Ei) has been generated.,

2. Control method according to claim 1, in which at least two separate secondary injections (I2) of fuel into the combustion chamber are controlled at said expansion time (TD).

3. Control method according to claim 1 or 2, in which a step of acquiring operating parameters of the internal combustion engine (1) is provided and in which said step of controlling at least one secondary injection (I2) is implemented only if the operating parameters meet at least one predetermined condition.

4. A method of driving according to claim 3, wherein said at least a predetermined condition is that a load and / or speed of the internal combustion engine is within a predetermined range.

5. A control method according to claim 3 or 4, wherein said at least one condition is that a temperature (T83, Tg) relative to the temperature of the catalyst (83) is within a predetermined range.

6. Control method according to one of claims 3 to 5, in which, when the operating parameters meet each predetermined condition, the secondary injection step is implemented at each expansion time (TD), for each cylinder (11).

7. Control method according to one of claims 1 to 6, in which the quantity of fuel injected during the steps of controlling the main and secondary injections and / or the quantity of fresh air admitted into the combustion chamber is regulated so that the richness of the burnt gases remains substantially equal to 1.

8. Control method according to one of claims 1 to 7, in which, the internal combustion engine (1) comprising a crankshaft, the step of controlling each secondary injection is implemented when the crankshaft has performed a rotation of between 20° and 60° after the start of the expansion time (TD).

9. Four-stroke internal combustion engine (1) with spark ignition, comprising: - at least one cylinder (111) delimiting a combustion chamber, - a fresh air intake line (20) opening into the combustion chamber and which comprises a compressor (22), - an exhaust line (80) for burnt gases outside the combustion chamber which comprises a turbine (82) adapted to rotate the compressor (22) and a catalyst (83) located upstream of the turbine (82), - an ignition circuit which comprises a spark plug (70) opening into each cylinder (11) and which is adapted to generate at least one spark (EJ, and - a circuit (60) for injecting fuel into the combustion chamber, characterized in that it comprises a computer programmed to implement a control method according to one of claims 1 to 8.

10. Motor vehicle comprising an internal combustion engine (1) according to claim 9.

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