Method for controlling a four-stroke internal combustion engine

Abstract

A method for controlling a four-times spark-ignition internal combustion engine (1) is comprising: - at least one cylinder (11), - a fresh air intake line (20) comprising a compressor (22), - a burnt gas exhaust line (80) comprising a catalyst (83) followed by a turbine (82), an ignition circuit that includes a spark plug (70) in each cylinder (11), - a fuel injection circuit (60), the method for controlling comprising a stage of acquiring an engine control instruction and a stage of main fuel injection at each intake time according to the acquired control instruction. The method further comprises, when said control instruction requires acceleration: - a stage of acquiring operating parameters of the engine, and - a stage of secondary injection of fuel at the expansion time, after the spark has been generated.

Description

DESCRIPTIONMETHOD FOR CONTROLLING A FOUR-STROKE INTERNAL COMBUSTION ENGINETechnical 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 called intake, compression, expansion and exhaust, this engine comprising:- at least one cylinder delimiting a combustion chamber,- a fresh air intake line opening outwards into the combustion chamber and comprising a compressor,- an exhaust line for burnt gases outside the combustion chamber which comprises, on the one hand, a turbine adapted to drive the compressor, and, on the other hand, an emission control catalyst for the burnt gases, located upstream of the turbine,- an ignition circuit which comprises a spark plug opening outwards into each cylinder and which is adapted to generate at least one spark at each compression or expansion time, and- a fuel injection circuit in the combustion chamber.

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

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

[0005] In an increasingly restrictive legislative framework and with a view to preserving the environment, technical solutions are currently being sought to improve the operating mode of internal combustion engines, in particular to reduce the level of pollutants contained in the burnt gases (combustion gases) emitted by the engines into the atmosphere.

[0006] To reduce these polluting emissions, a turbocharged internal combustion engine generally comprises, in its exhaust line, a turbine followed by a combustion gas emission control catalyst, in particular a three-way catalyst in the case of a spark-ignition engine, wherein chemical reactions occur in order to transform polluting compounds into compounds with no effect on health.

[0007] Such a catalyst works optimally when its temperature is above about 350°C. On the other hand, it has greatly reduced performance at room temperature, just after the cold start of the engine, and in particular below 150°C. As a result, most of the pollutantsreleased to the atmosphere are emitted within minutes of the cold start phase of the engine.

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

[0009] One solution for improving the efficiency of the catalyst would then be to size it according to its performance at low temperatures, by increasing its size. Efficiency refers to the percentage of pollutant compounds of a given type entering the catalyst that it actually converts into harmless compounds. For example, for a three-way catalyst, we talk about the efficiency of the catalyst in terms of oxidation of carbon monoxide CO or unburnt 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 seems difficult to limit the phenomenon of polluting emissions 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 speed of temperature rise of the catalyst after cold start of the engine 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 is indeed thermally inert and causes load losses which lead to a drop in the temperature of the burnt gases due to their expansion).

[0013] However, this solution has the disadvantage that the response time of the turbocharger, especially during acceleration phases, increases significantly. This response time problem arises from the thermal inertia of the catalyst and the load losses generated by this catalyst on the burnt gases. Indeed, the burnt gases leaving the catalyst have a restricted energy that does not allow them to operate the turbine as fast as desired.

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

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

[0016] In order to remedy the aforementioned drawbacks of the prior art, the present invention proposes to modify the sequence (or "pattern") of fuel injection into the combustion chamber in order, during acceleration phases, to very rapidly 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, wherein there is provided, when the control instruction requires an acceleration of the engine, a stage of controlling a secondary injection of fuel into the combustion chamber at the expansion time, after the spark has been generated.

[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. Therefore, this excess fuel is not burned in the cylinders but is discharged into the exhaust line. Unburnt hydrocarbons therefore reach the catalyst where they can generate a highly exothermic reaction very quickly increasing the enthalpy of the burnt gases leaving this catalyst and passing through the turbine.

[0019] In other words, when the acceleration request exceeds a predetermined threshold and it is therefore desired that the turbine rapidly rises in load, it is thus possible to inject fuel and oxygen into the catalyst so that the gases leaving it have a speed favourable to this rapid charging.

[0020] Other advantageous and non-limiting features of the method for controlling according to the invention, taken individually or according to all technically possible combinations, are as follows:- at least two separate secondary injections of fuel into the combustion chamber are controlled at said expansion time;- there is provided a stage of acquiring operating parameters of the internal combustion engine, and said stage 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 stage is implemented at each expansion time, for each cylinder;- the amount of fuel injected during the main and secondary injection control stages and / or the amount 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 stage of controlling each secondary injection is implemented when the crankshaft has rotated 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 method for controlling as mentioned above.

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

[0023] Of course, the various features, alternatives and forms of carrying out the invention may be associated with each other in various combinations as long as they are not incompatible or mutually exclusive.Detailed description of the invention

[0024] The following description with reference to the appended drawings, given as nonlimiting examples, will make it clear what the invention consists of and how it can be carried out.

[0025] On the appended drawings:

[0026] [Fig. 1] is a schematic view of an internal combustion engine according to the invention;

[0027] [Fig. 2] is a graph illustrating the four operating modes of the internal combustion engine of Figure 1 ; and

[0028] [Fig. 3] shows several graphs, illustrating in a synchronised manner, the variations of parameters of the internal combustion engine of Figure 1 , during a transient acceleration phase.

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

[0030] Figure 1 shows diagrammatically an internal combustion engine 1 equipped with a motor vehicle.

[0031] It could be a motor vehicle with hybrid propulsion, but it will be considered here as a purely thermal propulsion 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 the topby 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 sparkignition type (operating for example on petrol). Consequently, it comprises an ignition circuit which comprises in particular spark plugs 70 each opening outwards 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 draws fresh air from the atmosphere and which opens outwards 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 box 24, which makes it possible to regulate the flow of fresh air opening outwards in the air distributor 25.

[0035] At the outlet of the cylinders 1 1 , the internal combustion engine 1 comprises an exhaust line 80 which extends from an exhaust manifold 81 into which the gases that have been previously burned in the cylinders 11 open outwards, to an exhaust silencer 87 making it possible to expand the burnt gases before they are discharged into the atmosphere. It further comprises, in the direction of flow of the burnt gases, a catalyst 83 for the treatment of 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, catalyst 83 is qualified as a "three-way" catalyst in that it is intended to oxidise mainly unburnt hydrocarbons (HC) and carbon monoxide (CO) contained in the burnt gases, as well as to reduce nitrogen oxides (NOx).

[0039] The internal combustion engine 1 can also comprise one or more partial recirculation lines for the burnt gases at the intake (commonly known as lines of EGR for: Exhaust Gas Recirculation), starting in the exhaust line 80 and opening outwards into the intake line 20. These lines are not shown here.

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

[0041] Thanks to the position of the catalyst 83 upstream of the turbine 82, at the cold start of the engine, the temperature of the catalyst increases rapidly, which makes it possible to start the latter rapidly and therefore to ensure as quickly as possible an effective treatment of the burnt gases. By "starting" is meant the fact that the catalyst temperature increases until reaching a minimum temperature threshold at which its conversion efficiency with respect to the various pollutant types 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, in the acceleration phase, when the engine goes 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 efficient will be prolonged. Indeed, when the catalyst is cold or lukewarm (i.e. started but at a temperature of less than 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 for reducing the latency time of the turbine.

[0044] This solution consists in causing a rapid heating of catalyst 83 by supplying unburnt hydrocarbons and oxygen, via cylinders 11 .

[0045] As shown in Figure 1 , to thus 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 flow 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] In this respect, it will be recalled that the concept of richness is defined by the ratio between the "effective proportion of fuel in the gases" with respect to the "stoichiometric proportion of fuel in the gases".

[0049] The notion of "proportion of fuel in the gases" corresponds more precisely to the ratio between the mass flow rate of fuel with respect to the mass flow rate of air.

[0050] Provision could be made for the richness downstream of the catalyst 83 to be calculated using a mathematical model, as a function of various exogenous parameters, such as the speed of the engine, its load, its temperature, etc. Here, as shown in Figure 1 , it will be preferable to use a physical richness probe, for example an oxygen probe of the proportional type.

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

[0052] In this regard, the notion of the rate of depression of this pedal will be defined as the ratio between the position of the accelerator pedal and the total stroke enjoyed by this pedal. This rate of depression therefore forms an instruction to control 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] Here, a first temperature sensor 86 located in the catalyst 83 and a second temperature sensor 88 located at the inlet of the turbine 82 are provided. Alternatively, only one of these two sensors could be used. And alternatively, the measurements of 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] In addition, a sensor adapted to measure the speed of the internal combustion engine, and means for determining the load of this engine, are provided in a very conventional manner.

[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 computer to implement the method 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, and then burnt 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 particulate filter 84 and then expanded again in the exhaust silencer 87 before being discharged into the atmosphere.

[0060] The internal combustion engine 1 here operates on a four-stroke cycle. Thus, as shown in Figure 2, when each piston reciprocates in its cylinder 11 and causes the crankshaft to rotate, this engine is arranged such that:- during a first phase of descent of the piston, the cylinder 11 admits a mixture of fresh air and fuel, known as the intake time Ti (for the cylinder 1 1 in question, the crankshaft rotates during this time from 0 to 180°),- during a second piston raising phase, the admitted mixture compresses and combustion is initiated by ignition, known as the compression time Tc(the crankshaft rotating during this time by 180 to 360°),- during a third phase of descent of the piston, the compressed mixture burns and expands in the cylinder, known as the expansion time TExP. or explosion (the crankshaft rotating during this time from 360 to 540°),- during a fourth piston raising phase, the burnt mixture is discharged from the cylinder, known as the exhaust time TExh (the crankshaft rotating during this time from 540 to 720°).

[0061] The opening of the intake valve (throttle box) 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, depending in particular on the rate of depression of the accelerator pedal and the speed of the engine.

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

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

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

[0065] According to the control instruction received and the operating point of the engine, the computer 100 selects either a standard mode of calculation of the control instructions, or a particular mode of calculation, which is more precisely the object of the present invention and occurs during particular phases of acceleration. Hereinafter referred to as "standard mode" and "special 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 setpoint for controlling the intake valve 24. The idea is that the intake line 20 sucks in a sufficient flow of fresh air so that the internal combustion engine can develop the required torque (to move the vehicle forward and ensure the other needs of the vehicle - air conditioning, etc.). This deduction is made by means of a first mapping.

[0067] In this standard mode, the computer controls the fuel injectors 64 using a closed control loop according to which:- the richness value of the intake mixture is evaluated using the lambda probe 85, and- the quantity of fuel injected into each cylinder 1 1 at 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 amount of fuel injected at 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 1operates at low load and / or low speed, the temperature of the catalyst 83 stabilises at a reduced temperature.

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

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

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

[0073] The first condition is that the internal combustion engine 1 accelerates. This condition can for example be verified if the accelerator pedal depression rate increases at a speed above a threshold. In case that the vehicle is operating in an automated way, 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 lukewarm 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 temperature probes 86, 88 is below a predetermined threshold (for example 300°C). It could be verified otherwise, for example if the engine speed is stabilised at a low value for a time greater than a predetermined time threshold.

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

[0076] When the required conditions are met, the computer switches to special mode. Therefore, it controls the intake valve 24 so that it opens more than in standard mode and the fuel injectors 64 so as to inject fuel after the spark Si. 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 Figure 2, the idea is indeed to keep a main injection of fuel to satisfy the torque demand emitted by the driver via his accelerator pedal, and to add at least one injection of secondary fuel I2 later, so that this excess fuel does not burn in the combustion chamber but in the catalyst 83, with oxygen not having burnt 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 Figure 2, during each operating mode, a main fuel injection is carried out during the intake time Ti, and at least one secondary fuel injection l2is carried out during the expansion time TExp. The secondary injection(s) l2are carried out after thespark Si is formed by the spark plug (this spark being generated at the end of the compression time Tcor at the beginning of the expansion time TExp).

[0079] Thus, the unburnt hydrocarbons coming from the secondary injection(s), and the excess oxygen admitted into the cylinders can then react together within the catalyst 83 in a very exothermic manner, which makes it possible to very rapidly 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 rapidly rise to rpm, which reduces its reaction time.

[0080] It is possible here to 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 is to maintain the same main injection duration when switching from the standard mode to the special mode, and to perform secondary injections of predetermined durations. Thus, the torque demand can continue to be satisfied during this transition. In parallel, the opening of the intake valve 24 can then be regulated so as to maintain a richness of the burnt gases equal to 1. It can then be planned to increase or decrease the main injection time , depending on the 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 can 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 minimising the response time of the turbine 82.

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

[0086] "Separate" means that it is planned to control stopping and then resuming the fuel injection, allowing a predetermined time to pass between these two consecutive injections. This duration is at least 250 microseconds.

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

[0088] These secondary injections must not be carried out too early in the expansion time TEXP, 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 beinjected in the direction of the piston (when it is high in the cylinder 1 1 ) rather than on the wall of the cylinder 1 1 , to prevent it from mixing with the oil contained in the engine. If injected too late, when the burnt gas temperature has already dropped, it would also not vaporise properly in the burnt gas and would not mix well with it.

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

[0090] Figure 3 shows the variations of different engine parameters during an acceleration phase from a lightly loaded (low enthalpy) operating point, at a time ti.

[0091] Before this time ti, the internal combustion engine 1 was controlled in a stabilised manner, with the accelerator pedal slightly depressed (here at a depression rate Dacc equal to 10% of its total stroke).

[0092] Since this depression rate did not increase, the standard mode was selected (the boolean p of activation of the special 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 Tgof the burnt gases remained fairly low.

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

[0096] At time ti, the driver suddenly and abruptly depresses the accelerator pedal, so that the latter is more depressed (here at a depression rate Dacc equal to 60% of its total stroke).

[0097] The aforementioned conditions being then met (strong acceleration and lukewarm catalyst), the special mode is selected (the boolean therefore changes to one).

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

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

[0100] First of all, it is observed that the temperature Tgof the burnt gases between the catalyst 83 and the turbine 82 increases very rapidly, due to the aforementioned exothermic reactions. Therefore, the temperature T83 of the catalyst 83 also increases very rapidly. The same applies to the torque Cm delivered by the engine, since the turbine accelerates much faster than it would in standard mode.

[0101] It is then preferable to exit the standard mode at a time t2, i.e. as soon as one or other of the following three conditions is no longer fulfilled.

[0102] The first condition is that the rate of depression of the accelerator pedal and / or thevariation of this rate remains greater than a threshold. For example, this condition will 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 Tiim, corresponding to the temperature threshold beyond which it is considered that the catalyst 83 may degrade.

[0104] The third condition will be that the temperature Tgof the burnt gases downstream of the catalyst 83 remains below a threshold. This threshold will be chosen equal to a percentage of the temperature that could be reached in stabilised 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 optimise the load of turbine 82 before returning to standard mode, and- not too high so as not to significantly increase the fuel consumption of the engine (the increase in temperature of the gases being asymptotic, the secondary injections further promote this increase when the temperature of the burnt gases is far from the temperature that could be reached in stabilised mode).

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

[0107] The present invention is in no way limited to the mode described and shown, but a person skilled in the art will know how to make any variant thereof in accordance with the invention.

[0108] Typically, in a special mode, provision could be made not to regulate the richness to 1 in a closed loop, but to use a mapping of the opening of the fuel intake and injection valve which makes it possible a priori to maintain a richness of the burnt gases close to 1 .

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

Claims

CLAIMS

1. Method for controlling an internal combustion engine (1 ) of the four-stroke type with four times of intake (Ti), compression (Tc), expansion (TExp) and exhaust (TE), said internal combustion engine (1 ) comprising:- at least one cylinder (11 ) delimiting a combustion chamber,- a fresh air intake line (20) opening outwards 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 drive the compressor (22) in rotation, and, on the other hand, a catalyst (83) located upstream of the turbine (82),- an ignition circuit which comprises a spark plug (70) opening outwards into each cylinder (1 1 ) and which is adapted to generate at least one spark (Si) at each compression time (Tc) or expansion time (TExp), and- a fuel injection circuit (60) in the combustion chamber, the method for controlling comprising a stage of acquiring a control instruction of the internal combustion engine (1 ) and a stage of controlling a main injection (h) of fuel into the combustion chamber at each intake time (T i) according to the acquired control instruction, characterised in that it further comprises, when the control instruction requires acceleration, a stage of controlling at least one secondary injection (l2) of fuel into the combustion chamber at the expansion time (TExp), after the spark (Si) has been generated.

2. Method for controlling according to claim 1 , wherein at least two separate secondary injections (l2) of fuel into the combustion chamber are controlled at said expansion time (TExp).

3. Method for controlling according to claim 1 or 2, wherein there is provided a stage of acquiring operating parameters of the internal combustion engine (1 ) and wherein said stage of controlling at least one secondary injection (l2) is implemented only if the operating parameters meet at least one predetermined condition.

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

5. Method for controlling according to claim 3 or 4, wherein said at least one condition is that a temperature (T83, Tg) relating to the temperature of the catalyst (83) is withina predetermined range.

6. Method for controlling according to one of claims 3 to 5, wherein, when the operating parameters meet each predetermined condition, the secondary injection stage is carried out at each expansion time (TExp), for each cylinder (1 1 ).

7. Method for controlling according to one of claims 1 to 6, wherein the amount of fuel injected during the main and secondary injection control stages and / or the amount of fresh air admitted into the combustion chamber is regulated so that the richness of the burnt gases remains substantially equal to 1 .

8. Method for controlling according to one of claims 1 to 7, wherein, the internal combustion engine (1 ) comprising a crankshaft, the stage of controlling each secondary injection is implemented when the crankshaft has made a rotation between 20° and 60° after the start of the expansion time (TExp).

9. Four-times spark-ignition internal combustion engine (1 ), comprising:- at least one cylinder (11 1 ) delimiting a combustion chamber,- a fresh air intake line (20) opening outwards into the combustion chamber and which comprises a compressor (22),- a burnt gas exhaust line (80) 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 outwards into each cylinder (11 ) and which is adapted to generate at least one spark (Si), and- a fuel injection circuit (60) in the combustion chamber, characterised in that it comprises a computer programmed to implement a method for controlling according to one of claims 1 to 8.

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

Images