Method and system for controlling a spark-ignition internal combustion engine configured to detect and eliminate spark plug fouling

Abstract

Method (100) for controlling an internal combustion engine comprising at least one cylinder comprising a spark plug. The method (100) comprising:- a step (101) of detecting combustion problems on at least one cylinder;- a verification step (102), in which it is verified whether the engine operating point is in a critical speed and load zone for spark plug fouling; and- a step (103) of defouling the spark plugs configured to increase the pressure and temperature levels in the given cylinder in order to exceed a temperature threshold, for example greater than or equal to 500°C. Figure for abstract: Fig 6

Description

Title of the invention: Method and system for controlling a spark-ignition internal combustion engine configured to detect and eliminate spark plug fouling

[0001] The present invention relates to the field of internal combustion engines, and in particular spark ignition engines.

[0002] More particularly, the invention relates to the elimination of fouling of spark plugs in spark ignition engines.

[0003] Generally, in a supercharged internal combustion engine comprising cylinders supercharged by a turbocharger, each of the cylinders is equipped with a spark plug used to trigger combustion.

[0004] A spark plug comprises, in a known manner, a connection tip through which the current arrives and extended by an insulator, a central electrode and a ground electrode forming the functional part of the spark plug which extends partly into the combustion chamber. It is between these two electrodes that the spark is formed allowing ignition.

[0005] Figures 1A and 1B respectively illustrate a spark plug in a normal operating state and a spark plug in a fouled state.

[0006] In [Fig.lA], the electrodes 2, 3, of the spark plug 1 are not dirty and the spark can be produced efficiently.

[0007] In [Fig. 1B], a deposit of fouling particles is observed, such as for example an amalgam of soot, oil, fuel, etc. In such a case, the energy of the spark is too low for ignition to be carried out efficiently. In the case where the entire space between the two electrodes is filled by the fouling particles, a short circuit is created, which prevents any spark and the cylinder concerned is not ignited.

[0008] This involves combustion problems on the cylinder(s) concerned, such as difficulties or even an inability to start the engine, a lack of torque, engine speed instabilities, an engine running on some of its cylinders.

[0009] The typical usage profile that generates spark plug fouling is a succession of short journeys, with the engine cold, at low speeds, without applying heavy loads.

[0010] On the one hand, the succession of cold starts will generate fouling of the spark plugs because, under these conditions, the air-fuel mixture is rich, i.e. richness greater than 1, to ensure a good start then a stable combustion, with high concentrations of particles and unburned fuel which will foul the spark plugs.

[0011] On the other hand, the engine remains in a speed / load zone where the gas temperatures within the combustion chamber are relatively low. The spark plug fouling will therefore not be able to be eliminated naturally because a minimum temperature of 500°C is required to burn off the fouling particle deposits. A motorway journey will burn off the fouling particle deposits automatically.

[0012] In the event of severe fouling of the spark plugs, they will need to be changed.

[0013] However, this does not solve the problem of fouling over time, since due to its use, the spark plugs will become fouled again and the user will have to replace them again.

[0014] There is a need to address the problem of spark plug fouling in a robust manner.

[0015] Document FR 2 680 833 - A1 is known, which proposes a method for detecting fouling of a spark plug connected to a spark ignition system comprising a coil comprising a primary circuit and a secondary circuit in which a primary current and a secondary current circulate respectively. This document proposes calculating a slope of the secondary voltage curve as a function of the secondary current and developing a defouling signal when said slope is greater than or equal to zero.

[0016] However, this document does not specify the defouling strategy.

[0017] Document EP 961 029 - B1 is also known, which discloses a method for controlling an internal combustion engine of a motor vehicle, the ignition system of which by spark plugs connected to an induction coil and the injection of fuel into the cylinders are controlled by an electronic computer. The method comprises a phase of detection, by the computer, of the fouling of a spark plug and of comparison of this fouling with an alert threshold. In the event of fouling being detected, the computer temporarily modifies the ignition advance control and / or the injection time on the cylinder(s) associated with the fouled spark plugs.

[0018] However, such a method is not satisfactory in terms of defouling the spark plugs.

[0019] The present invention aims to eliminate spark plug fouling reliably and at low cost.

[0020] The subject of the present invention is a method for controlling an internal combustion engine comprising at least one cylinder, an intake circuit comprising at least in the direction of circulation of fresh air, a compressor of a turbocharger, a heat exchanger, a throttle body or a valve gas intake manifold into the engine, and a fresh air intake manifold supplied with fresh air, each cylinder comprising a spark plug comprising a first electrode and a second electrode extending partly into the combustion chamber of the associated cylinder, in particular to allow the creation of a spark aimed at igniting said cylinder.

[0021] The method comprises: - a step of detecting combustion problems on at least one cylinder during which a torque generated by each of the cylinders is calculated from an analysis of the instantaneous speed, the torque is compared with a torque setpoint to obtain a difference between the torque setpoint and the calculated torque and this difference is compared with a critical threshold value.

[0022] If the difference between the torque setpoint and the calculated torque is greater than a critical threshold value, it is considered that combustion problems are detected.

[0023] The method further comprises a verification step, in which it is verified whether the engine operating point is in a critical speed and load zone for spark plug fouling corresponding to a speed and load zone in which the gas temperatures in the combustion chamber are less than 500°C.

[0024] The term “critical speed and load zone” means a zone in which the speed is less than or equal to 2500 revolutions per minute and in which the load is less than or equal to 50% of the full load value.

[0025] If the difference between the torque setpoint and the calculated torque is greater than a critical threshold value and the operating point of the engine is located in the critical speed and load zone, the method activates a step of defouling the spark plugs, i.e. of eliminating the deposit of fouling particles on the electrodes, configured to increase the pressure and temperature levels in the given cylinder in order to exceed a temperature threshold, for example greater than or equal to 500°C, making it possible to eliminate the deposits of fouling particles.

[0026] During the spark plug cleaning step, an ignition over-advance instruction, greater than the optimal advance, is transmitted to an engine control system to increase the pressure and temperature levels in the cylinder.

[0027] By "over-advance" on ignition, we mean a degraded efficiency less than 1, of preferably less than or equal to 0.8.

[0028] For example, the over-advance level is predetermined during tests on each of the operating points in the critical speed and load zone to reach a temperature greater than or equal to 500°C and is mapped in the control system as a function of the speed and load.

[0029] Advantageously, simultaneously or subsequently to the step of cleaning the spark plugs, a throttle body opening instruction is transmitted to allow more air to enter the engine during the transmission of an ignition timing advance instruction.

[0030] The pressure of the fresh air in the intake manifold will thus increase and therefore the pressure levels of the gases in the cylinder increase in the same way.

[0031] According to another aspect, the invention relates to an electronic control unit for an internal combustion engine comprising at least one cylinder, an intake circuit comprising at least in the direction of circulation of fresh air, a compressor of a turbocharger, a heat exchanger, a throttle body or a valve for admitting gases into the engine, and a fresh air intake manifold supplied with fresh air, each cylinder comprising a spark plug comprising a first electrode and a second electrode extending partly into the combustion chamber of the associated cylinder, in particular to allow the creation of a spark aimed at igniting said cylinder.

[0032] The electronic control unit comprises an engine control system comprising: - a module for detecting combustion problems on at least one cylinder, configured to calculate a torque generated by each of the cylinders from an analysis of the instantaneous speed, compare the torque with a torque setpoint to obtain a difference between the torque setpoint and the calculated torque and compare this difference with a critical threshold value.

[0033] If the difference between the torque setpoint and the calculated torque is greater than a critical threshold value, the combustion problems are considered to be becoming critical.

[0034] The engine control system further comprises a verification module, which verifies whether the engine operating point is in a critical speed and load zone for spark plug fouling in which the gas temperatures in the combustion chamber are below 500°C.

[0035] The engine control system further comprises a spark plug defouling module, i.e. a module for removing the deposit of fouling particles on the electrodes, configured to increase the pressure and temperature levels in the given cylinder when the difference between the torque setpoint and the calculated torque is greater than a critical threshold value and the engine operating point is in the critical speed and load zone in order to exceed a temperature threshold, for example greater than or equal to 500°C, making it possible to remove the deposits of fouling particles; and - an ignition timing control module configured to transmit to the control system an ignition timing setpoint, greater than the optimum timing, to increase the pressure and temperature levels in the cylinder.

[0036] Advantageously, the control system is configured to transmit a throttle body opening instruction to allow more air to enter the engine when the control module transmits an ignition over-advance instruction.

[0037] The pressure of the fresh air in the intake manifold will thus increase and therefore the pressure levels of the gases in the cylinder increase in the same way.

[0038] According to another aspect, the invention relates to a motor vehicle comprising a spark-ignition internal combustion engine and an electronic control unit as described above.

[0039] 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:

[0040] [Fig.lA], [Fig.lB] schematically illustrate respectively a spark plug in a normal operating state and a spark plug in a fouled state;

[0041] [Fig.2] represents, in a very schematic manner, an example of the structure of an internal combustion engine of a motor vehicle comprising a control unit comprising a control system according to the invention configured to detect and eliminate fouling of a spark plug;

[0042] [Fig.3] represents for three separate cylinders, the torque calculated in relation to the torque setpoint;

[0043] [Fig.4] illustrates the evolution of the advance efficiency as a function of the advance applied at a given operating point of the engine;

[0044] [Fig.5A], [Fig.5B] illustrate the comparison at an operating point of the critical zone respectively of the pressure and temperature levels of the gases in a given cylinder as a function of the crankshaft angle between the nominal advance setting and the over-advance setting by the control system according to the invention;

[0045] [Fig.6] represents the block diagram of a control method implemented by the system of [Fig.2] configured to detect and eliminate fouling of a spark plug.

[0046] In Figure 1, there is shown, schematically, the general structure of an internal combustion engine 10, in particular of a motor vehicle, of the spark ignition type operating for example on gasoline or alternatively with alcohol, or liquefied gas, called "LPG", etc.

[0047] These architectures are given as examples and do not limit the invention to the sole configuration to which the motor control according to the invention can be applied.

[0048] In the illustrated example, the internal combustion engine 10 comprises, in a non-limiting manner, three cylinders 12 in line, a fresh air intake manifold 14, an exhaust manifold 16 and a turbo-compression system 18.

[0049] The cylinders 12 are supplied with air via the intake manifold 14, or intake distributor, itself supplied by a pipe 20 provided with an air filter 22 and the compressor 18b of the turbocharger 18 of the engine 10.

[0050] Each cylinder 12 is supplied with fuel, for example gasoline type.

[0051] In a known manner, the turbocharger 18 essentially comprises a turbine 18a driven by the exhaust gases and a compressor 18b mounted on the same axis or shaft as the turbine 18a and providing compression of the air distributed by the air filter 22, with the aim of increasing the quantity (mass flow rate) of air admitted into the cylinders 12 of the engine 10. The turbine 18a may be of the “variable geometry” type, that is to say that the turbine wheel is equipped with blades with variable inclination in order to modulate the quantity of energy taken from the exhaust gases, and thus the boost pressure.

[0052] A heat exchanger 30 is placed after the outlet of the compressor 18b equipping the supply line 14a of the intake manifold 14 with fresh air.

[0053] The internal combustion engine 10 thus comprises an intake circuit Ca, an exhaust circuit Ce and a fuel injection circuit Ci.

[0054] The intake circuit Ca comprises, from upstream to downstream in the direction of air circulation:

[0055] - the air filter 22 or air box;

[0056] - the compressor 18b of the turbocharger 18 configured to compress the bleed air in the external atmosphere and where appropriate low pressure recycled exhaust gases, as will be described later;

[0057] - the heat exchanger 30 configured to cool the intake gases corresponding to a mixture of fresh air and recycled gases, after their compression in the compressor 18b;

[0058] - a throttle body 28 or a gas intake valve in the engine; and

[0059] - the intake manifold 14.

[0060] The heat exchanger 30 is a cooler of the so-called “supercharged” intake gases, corresponding, here, to an air-water exchanger, called “water charged air cooler” in English terms. The terms “heat exchanger 30” and “charge air cooler 30” designate, subsequently, the same element. Alternatively, it may be an air-air cooler.

[0061] The exhaust circuit Ce comprises, from upstream to downstream in the direction of circulation of the burnt gases:

[0062] - the exhaust manifold 16;

[0063] - the turbine 18a of the turbocharger 18 configured to take energy from the exhaust gases passing through it, said expansion energy being transmitted to the compressor 18b via the common shaft, for the compression of the intake gases; and

[0064] - a system 40 for depolluting the combustion gases of the engine.

[0065] As regards the exhaust manifold 16, the latter recovers the exhaust gases resulting from the combustion and evacuates them to the outside, via a gas exhaust duct 32 opening onto the turbine 18a of the turbocharger 18 and via an exhaust line 34 mounted downstream of said turbine 18a.

[0066] By way of non-limiting example, the system 40 for depolluting the combustion gases of the engine comprises a first device 42 comprising a three-way catalyst 42a.

[0067] The gas depollution system 40 further comprises a second device 44 which is here a fine particle filter, and an exhaust pipe 45 mounted at the outlet of the second depollution device 44 and opening outwards.

[0068] As illustrated, the engine 10 does not include a partial recirculation circuit for the exhaust gases at the intake, called an “EGR” circuit (“exhaust gas recirculation” in English terms).

[0069] Alternatively, it could be provided that the engine comprises such an exhaust gas recirculation circuit, in particular at low pressure, called “EGR BP”, originating at a point in the exhaust line 34, here, in the exhaust pipe 45, downstream of said turbine 18a, and in particular downstream of the gas depollution system 40 and returns the exhaust gases to a point in the fresh air supply pipe 20, upstream of the compressor 18b of the turbocharger 18.

[0070] Alternatively, the low-pressure exhaust gas recirculation circuit could originate at the outlet of the turbine 18a, or downstream of only part of the gas depollution system 40, for example between the first and second depollution devices 42, 44.

[0071] By way of non-limiting example, the engine is associated with a fuel circuit comprising, for example, fuel injectors (not referenced) injecting gasoline directly into each cylinder from a fuel tank (not shown).

[0072] The engine 10 may also comprise, in a non-limiting manner, a purge circuit (not shown) for fuel vapors.

[0073] Each cylinder 12 comprises a spark plug 13 comprising a first electrode and a second electrode (not shown) extending partly into the combustion chamber of the associated cylinder 12 to allow the creation of a spark aimed at the ignition of said cylinder 12.

[0074] The engine 10 comprises an engine computer (not shown) and an electronic control unit ECU 50 embedded in the engine computer.

[0075] The electronic control unit ECU 50 comprises a control system 60 configured to control the various elements of the internal combustion engine and in particular the ignition advance.

[0076] The control system 60 receives data collected by sensors at different locations of the engine or estimated, in particular the torque calculated on each of the cylinders 12.

[0077] The control system 60 could receive other data.

[0078] The control system 60 comprises a module 61 for detecting combustion problems on at least one cylinder 12.

[0079] Said detection module 61 is configured to calculate a torque C_calc generated by each of the cylinders 12 from an analysis of the instantaneous speed n, compare the torque C_calc with a torque setpoint C_cs to obtain a difference x% between the torque setpoint C_cs and the calculated torque C_calc and compare this difference x% with a critical threshold value e%.

[0080] The calculation of torque C_calc generated by each of the cylinders 12 from an analysis of the instantaneous speed n can, for example, be done in accordance with the teaching of publication FR 2 681 425 - AL

[0081] When the spark plug is fouled on a given cylinder 12 leading to less efficient combustion or even to cycles with misfires, known as "misfires", the calculated torque C_calc on this given cylinder will be lower than the torque setpoint C_cs, as can be seen in [Fig.3] which represents for three separate cylinders Cyll, Cyl2, Cyl3, the calculated torque C_calc compared to the torque setpoint C_cs.

[0082] If the difference x% between the torque setpoint C_cs and the calculated torque C_calc is greater than a critical threshold value e%, it is considered that the combustion problems become critical.

[0083] The control system 60 comprises a module 62 for checking whether the engine operating point is in a critical speed and load zone for spark plug fouling.

[0084] In the critical speed and load zone, the gas temperatures in the combustion chamber are below 500°C.

[0085] The term “critical speed and load zone” means a zone in which the speed is less than or equal to 2500 revolutions per minute and in which the load is less than or equal to 50% of the full load value.

[0086] The control system 60 further comprises a module 63 for defouling the spark plugs 13, i.e. for eliminating the deposit of fouling particles on the electrodes.

[0087] The module 63 for cleaning the spark plugs 13 is configured to increase the pressure and temperature levels in the cylinder 12 when the difference x% between the torque setpoint C_cs and the calculated torque C_calc is greater than a critical threshold value e% and the operating point of the engine is located in the critical speed and load zone in order to exceed a temperature threshold T_threshold, for example greater than or equal to 500°C, making it possible to eliminate deposits of fouling particles.

[0088] In order to increase the pressure and temperature levels in the cylinder, the defouling module 63 comprises a module 64 for controlling an ignition over-advance.

[0089] Currently, it is known to control an ignition advance. As can be seen in [Fig.4] illustrating for a given operating point the evolution of the advance efficiency Rend_Av as a function of the applied ignition advance Av_appl, the advance efficiency retranslates the impact of the advance on the engine efficiency, and therefore its fuel consumption. When the advance is optimal, Av_opt, the advance efficiency is equal to 1. When the advance is lower, i.e. lower than the optimal advance, we speak of under-advance, and when the advance is higher, i.e. higher than the optimal advance, we speak of over-advance. In these cases, the efficiency is degraded and lower than 1.

[0090] Nowadays, all engines operate at the optimum advance Av_opt or in the under-advance zone. Under-advance allows for rapid torque modulation. However, it reduces the gas temperature levels in the cylinder.

[0091] The ignition over-advance control module 64 is configured to operate in a currently unexploited area corresponding to an over-advance. This makes it possible to achieve an increase in the temperature and pressure of the gases in the cylinder 12, as can be seen in FIG. 5.

[0092] By “over-advance” on ignition, we mean a degraded efficiency less than 1, preferably less than or equal to 0.8.

[0093] In this case, the module 64 for controlling an over-advance on ignition transmits to the control system 60 an advance instruction Av_appl greater than the optimal advance Av_opt.

[0094] The over-advance level is predetermined during tests on each of the operating points of the critical speed and load zone to reach a temperature greater than or equal to 500°C and is mapped in the control system 60 as a function of the speed and the load.

[0095] The greater the ignition over-advance, the lower the advance efficiency, which generates a drop in the torque produced by the engine. In order to maintain the torque C_calc at the set value C_cs, the control system 60 transmits an instruction to open the throttle body 28 to allow more air to enter the engine. The pressure of the fresh air in the intake manifold 14 will thus increase and therefore the gas pressure levels in the cylinder 12 increase in the same way.

[0096] The control method 100 is configured to control the various elements of the internal combustion engine and in particular the ignition advance.

[0097] The control method 100 comprises a step 101 of detecting combustion problems on at least one cylinder 12.

[0098] During the detection step 101, a torque C_calc generated by each of the cylinders 12 is calculated from an analysis of the instantaneous speed n and the torque C_calc is compared with the torque setpoint C_cs to obtain a difference x% between the torque setpoint C_cs and the calculated torque C_calc.

[0099] This difference x% is then compared with a critical threshold value e%.

[0100] If the difference x% between the torque setpoint C_cs and the calculated torque C_calc is greater than the critical threshold value e%, combustion problems are considered to become critical.

[0101] The control method 100 comprises a verification step 102, in which it is verified whether the engine operating point is in a critical speed and load zone for spark plug fouling.

[0102] In the critical speed and load zone, the gas temperatures in the combustion chamber are below 500°C.

[0103] The term “critical speed and load zone” means a zone in which the speed is less than or equal to 2500 revolutions per minute and in which the load is less than or equal to 50% of full load.

[0104] The control method 100 further comprises a step 103 of defouling the spark plugs 13, i.e. of eliminating the deposit of fouling particles on the electrodes, when the engine operating point is in a critical speed and load zone for spark plug fouling and when the difference x% between the torque setpoint C_cs and the calculated torque C_calc is greater than a critical threshold value e%.

[0105] During step 103 of defouling the spark plugs 13, the pressure and temperature levels in the cylinder 12 are increased when the operating point of the engine is located in the critical speed and load zone in order to exceed a temperature threshold T_threshold, for example greater than or equal to 500°C, making it possible to eliminate the deposits of fouling particles.

[0106] In order to increase the pressure and temperature levels in the cylinder, an over-advance is ordered for the ignition. To do this, an advance instruction Av_appl greater than the optimal advance Av_opt is transmitted to the control system 60.

[0107] By “over-advance” on ignition, we mean a degraded efficiency less than 1, preferably less than or equal to 0.8.

[0108] The over-advance level is predetermined during tests on each of the operating points of the critical speed and load zone to reach a temperature greater than or equal to 500°C and is mapped in the control system 60 as a function of the speed and the load.

[0109] The greater the ignition over-advance, the lower the advance efficiency, which generates a drop in the torque produced by the engine. In order to maintain the torque C_calc at the set value C_cs, the method 100 further comprises a step 104 of transmitting an instruction to open the throttle body 28 to allow more air to enter the engine. The pressure of the fresh air in the intake manifold 14 will thus increase and therefore the gas pressure levels in the cylinder 12 increase in the same way.

[0110] Thanks to the invention, it is easy to detect and eliminate spark plug fouling reliably and at low cost.

Claims

1. Claims Method (100) for controlling an internal combustion engine (10) comprising at least one cylinder (12), an intake circuit (Ca) comprising at least in the direction of fresh air circulation, a compressor (18b) of a turbocharger (18), a heat exchanger (30), a throttle body (28), and a fresh air intake manifold (14) supplied with fresh air, each cylinder (12) comprising a spark plug (13) comprising a first electrode and a second electrode extending partly into the combustion chamber of the associated cylinder (12), the method (100) comprising: - a step (101) of detecting combustion problems on at least one cylinder (12) during which a torque (C_calc) generated by each of the cylinders (12) is calculated from an analysis of the instantaneous speed (n),we compare the torque (C_calc) with a torque setpoint (C_cs) to obtain a difference (x%) between the torque setpoint (C_cs) and the calculated torque (C_calc) and we compare this difference (x%) with a critical threshold value (e%), if the difference (x%) between the torque setpoint (C_cs) and the calculated torque (C_calc) is greater than a critical threshold value (e%), we consider that combustion problems are detected;, - a verification step (102), in which it is verified whether the engine operating point is in a critical speed and load zone for spark plug fouling corresponding to a speed and load zone in which the gas temperatures in the combustion chamber are less than 500°C; - if the difference (x%) between the torque setpoint (C_cs) and the calculated torque (C_calc) is greater than a critical threshold value (e%) and the operating point of the engine is located in the critical speed and load zone, the method (100) activates a step (103) of cleaning the spark plugs (13) configured to increase the pressure and temperature levels in the given cylinder (12) in order to exceed a temperature threshold, for example greater than or equal to 500°C; during the step (103) of cleaning the spark plugs (13), an ignition over-advance setpoint (Av_appl) is transmitted to an engine control system (60), greater than the optimal advance (Av_opt), in order to increase the pressure and temperature levels in the cylinder (12).

2. Method (100) according to claim 1, in which simultaneously or subsequently to the step (103) of cleaning the spark plugs (13), an instruction is transmitted to open the throttle body (28) to allow more air to enter the engine during the transmission of an ignition over-advance instruction.

3. Electronic control unit (ECU 50) of an internal combustion engine (10) comprising at least one cylinder (12), an intake circuit (Ca) comprising at least in the direction of fresh air circulation, a compressor (18b) of a turbocharger (18), a heat exchanger (30), a throttle body (28) and a fresh air intake manifold (14) supplied with fresh air, each cylinder (12) comprising a spark plug (13) comprising a first electrode and a second electrode extending partly into the combustion chamber of the associated cylinder (12), the electronic control unit (ECU 50) comprising an engine control system (60) comprising: - a module (61) for detecting combustion problems on at least one cylinder (12), configured to calculate a torque (C_calc) generated by each of the cylinders (12) from an analysis of the instantaneous speed (n),compare the torque (C_calc) with a torque setpoint (C_cs) to obtain a difference (x%) between the torque setpoint (C_cs) and the calculated torque (C_calc) and compare this difference (x%) with a critical threshold value (e%); if the difference (x%) between the torque setpoint (C_cs) and the calculated torque C_calc is greater than a critical threshold value (e%), it is considered that the combustion problems are detected; - a verification module (62),which checks whether the engine operating point is in a critical speed and load zone for spark plug fouling in which the gas temperatures in the combustion chamber are below 500°C; - a spark plug (13) defouling module (63) configured to increase the pressure and temperature levels in the given cylinder (12) when the difference (x%) between the torque setpoint (C_cs) and the calculated torque (C_calc) is greater than a critical threshold value (e%) and the engine operating point is in the speed zone and, critical load in order to exceed a temperature threshold, for example greater than or equal to 500°C; and - an ignition over-advance control module (64) configured to transmit to the control system (60) an ignition over-advance instruction (Av_appl), greater than the optimal advance (Av_opt), in order to increase the pressure and temperature levels in the cylinder (12).

4. Control unit according to claim 3, in which the control system (60) is configured to transmit a throttle body (28) opening instruction to bring more air into the engine when the control module (64) transmits an ignition over-advance instruction.

5. Motor vehicle comprising an electronic control unit according to claim 3 or 4.

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