Method and system for controlling the torque delivered during a gear change for a motor vehicle equipped with at least one exhaust gas recirculation system

Abstract

This method (40) for controlling the torque delivered during a gear ratio change by a motor vehicle internal combustion engine equipped with at least one partial exhaust gas recirculation system at the engine intake, comprises the following steps: determining a target torque value (C_target) necessary for the gear ratio change (step 41); determining a first torque value that the engine can produce, from its current operating point, by removing the ignition advance (step 42); determining a second torque value, lower than the current torque of the engine, from which it is possible to produce the target torque value (C_target) by resorting only to removing the ignition advance of the engine (step 45). Figure for abstract: Figure 5

Description

Title of the invention: Method and system for controlling the torque delivered during a gear change for a motor vehicle equipped with at least one exhaust gas recirculation system Technical field

[0001] The present invention relates to internal combustion engines of motor vehicles, provided with at least one circuit for partial recirculation of exhaust gases at the engine intake.

[0002] It relates in particular, in an application of the invention, to the management of the torque supplied by the engine in the event of a change of gear ratio. Previous techniques

[0003] On a motor vehicle equipped with an internal combustion engine, more particularly a spark-ignition engine, the depression of the engine's intake manifold, generally adjusted using a throttle body of the engine to obtain a certain mass flow of air allowing the production of engine torque, causes pumping losses which are induced by the pressure difference between the plenum of the intake manifold and the exhaust manifold of the engine.

[0004] [Fig. 1] represents the pressure-volume diagram and characterizes the operation of a conventional four-stroke cycle engine. The pumping losses correspond to the hatched area 2 which represents the work consumed by the engine, unlike the hatched area 1 which represents the work supplied by the engine. According to the conventional cycle of [Fig.l] representing the stages undergone by the gases in a cylinder of the engine, the intake stage (intake stroke) corresponds to segment AB, compression to segment BC, combustion to segment CD, expansion to segment DE and exhaust to segment EA.

[0005] In order to reduce the pumping losses of the engine, it is advantageous to increase the intake manifold pressure to a value as close as possible to the engine exhaust manifold pressure. Thus the gas pressure during the intake stage approaches the gas pressure in the exhaust phase and the amount of work consumed by the engine decreases.

[0006] Conventionally, the driver of the vehicle determines, by operating the accelerator pedal, an acceleration setpoint for the vehicle. From the acceleration setpoint and the engine speed, a computer defines an engine torque setpoint to be obtained to reach this acceleration setpoint. The torque setpoint is translated into an air mass flow setpoint Qair, into a value ignition advance generally optimizing efficiency, and in a richness setpoint generally equal to 1, which corresponds to the flow rate of the fuel which must be burned in stoichiometric proportions to obtain the torque while operating an engine depollution catalyst in its catalytic operating range in which it is capable of treating unburned hydrocarbons, carbon monoxide and nitrogen oxides.

[0007] Furthermore, when the vehicle is equipped with a partial exhaust gas recirculation circuit at the engine intake, a recycled gas mass flow rate setpoint Qegr is also defined at the intake which corresponds to the recycling rate to be applied to comply with the target fuel consumption. This exhaust gas recycling rate or EGR rate ("exhaust gas recirculation" in English) is defined as the ratio between the mass of reinjected exhaust gas entering per unit of time in the intake circuit and the total mass of gas entering per unit of time in the combustion chambers of the engine.

[0008] The sum of the air flow rate Qair and the recycled exhaust gas flow rate Qegr represents the total gas mass flow rate Qmot entering the engine, which is generally set by adjusting the position of a throttle body in the engine's air intake circuit so as to obtain a pressure value Pcol in the engine's intake manifold corresponding to the desired total flow rate.

[0009] An engine computer uses an air filling model, which makes it possible to determine the value of the minimum pressure of the intake manifold to meet the engine torque setpoint.

[0010] This filling model follows the following equation:

[0011] = C4WX120 (1) rclvl NX Cylinder capacity X

[0012] In which:

[0013] ^rdvl denotes the volumetric yield or “filling”, dimensionless;

[0014] Qmot denotes the total mass flow rate actually entering, in kg / s;

[0015] N denotes the speed, in revolutions / min;

[0016] Cylinder capacity means the cylinder capacity of the engine, in m3;

[0017] Pcol denotes the pressure in the intake manifold, in Pa;

[0018] Tcol, denotes the temperature in the intake manifold, in K; and

[0019] R denotes the mass constant of ideal gases for air equal to approximately 287.058 J / kgxK •

[0020] The term "filling" is defined as being equal to the ratio between the mass of air sucked in and the mass of air which could have entered considering only the total volume of the cylinders.

[0021] In all cases, the value of the efficiency ^rdvl depends on the regime N and the pressure in the intake manifold Pcol.

[0022] At partial load, that is to say when the need for air flow is low, the pressure in the intake manifold may, in the case of a naturally aspirated engine and if only air is admitted into the engine, be much lower than the atmospheric pressure corresponding to full load, which results in high pumping losses.

[0023] To reduce these pumping losses, it is necessary to increase the pressure in the intake manifold and bring it as close as possible to the value of the pressure in the exhaust manifold.

[0024] One way to increase the pressure in the intake manifold is to use exhaust gas recirculation or EGR.

[0025] This EGR process consists of taking gases from the exhaust and sending them to the intake, for example downstream of an engine air flow control valve. The supply of recycled exhaust gases to the intake makes it possible to increase the pressure in the engine intake manifold for the same air flow value necessary for producing torque, and thus makes it possible to reduce pumping losses and therefore improve engine efficiency and fuel consumption.

[0026] Conventionally, an engine ignition advance value is set so that ignition occurs a few moments before top dead center (TDC), in order to take into account the time required for combustion to develop.

[0027] Thus, to produce a given torque, an engine ignition advance value is generally set to a value equal to the optimal advance, or failing that to a value which is closest to the optimal advance without creating knocking, so as to maximize combustion efficiency, i.e. the advance chosen is that which maximizes the torque for the same air and fuel flow rate.

[0028] However, when changing gear ratio it is necessary for the engine torque to be temporarily brought to a very low torque, almost zero, which only compensates for the engine friction. In this case, advance withdrawals are carried out so as to very quickly reduce the torque value without modifying the position of the air circuit actuators such as the throttle body or EGR valve.

[0029] Indeed, to rapidly lower the torque, it is more efficient to modify the ignition advance rather than the position of an air flow control valve, because the response time for the torque to actually collapse is significantly lower when removing the advance.

[0030] Nevertheless, in the event of the addition of EGR in the combustion chamber, the combustion generally becomes slower and less stable than in the absence of EGR, so that it is difficult to collapse the torque in the event of a gear change, to carry out advance withdrawals without causing a combustion misfire, because the combustion risks becoming so slow under the effect of such under-advances that it is completely stopped.

[0031] [Fig.2] illustrates the combustion duration as a function of the EGR rate present in the combustion chamber. It will be noted that the combustion duration increases the higher the EGR rate, with combustion instabilities when the combustion cycle is completed before all of the enclosed fuel has been burned.

[0032] [Fig. 3] qualitatively illustrates the possible variation ranges of the ignition advance as a function of the EGR rates. The combustion efficiency corresponds to the engine torque which is obtained as a function of the ignition advance, at identical air flow and at richness 1. The peak of each curve corresponds to the best combustion efficiency and to the optimum advance for each EGR rate. All the curves are limited on their right by the knocking phenomenon and on their left by combustion instability, that is to say that by reducing or increasing the ignition advance, a low threshold is reached respectively from which the combustion becomes unstable and a high threshold from which the combustion becomes non-homogeneous with self-ignition of the gases not yet burned, characteristic of knocking.

[0033] As illustrated by curve 3 of [Fig.3] corresponding to an absence of EGR in the combustion chamber, it is possible to reduce the value of the ignition advance to modify the combustion efficiency, and in particular in the direction of reduction. Thus in the absence of EGR, the reduction in advance carried out in relation to the optimal advance makes it possible to reduce the torque produced by the engine almost instantly.

[0034] The problem is that the possible ranges of values ​​for the ignition advance are reduced as the EGR rate increases. For curves 3, 4 and 5 of [Fig.3], corresponding to respective EGR rates of 0%, 10% and 20%, the width of the interval 3a-3b is greater than the width of the interval 4a-4b, which is itself greater than the width of the interval 5a-5b. This means that there is less possibility of massively reducing the engine torque by withdrawals of advance, as the EGR rate increases. Thus, as illustrated by curve 5 of [Fig.3], for high EGR rates, the combustion stability limit (5a) is reached well before having succeeded in significantly reducing the torque.

[0035] In the methods known from the state of the art, the EGR rates are not reduced, so that the advance withdrawals which are carried out to collapse the torque to a value necessary for the gear ratio changes, generate a risk of combustion instabilities which can result in combustion misfires likely to degrade the operation of the catalyst and thus increase the emission of pollutants. Statement of the invention

[0036] In view of the above, the invention aims to reduce the risk of combustion instabilities during advance withdrawals which are carried out to collapse the torque to a value necessary for gear ratio changes, while maintaining the EGR rates at values ​​close to an optimal consumption setting.

[0037] The subject of the invention is a method for controlling the torque delivered during a gear change by an internal combustion engine of a motor vehicle equipped with at least one system for partial recirculation of exhaust gases at the intake.

[0038] The method comprises the following steps: - determination of a target torque value required for changing gear ratio; - determination of a first torque value that the engine can produce, from its current operating point, by removing the ignition advance; - determination of a second torque value, lower than the current engine torque, from which it is possible to produce the target torque value using only a reduction in engine ignition advance.

[0039] For example, the second torque value is obtained by reducing the mass flow rate of air entering the engine.

[0040] Advantageously, the reduction in the air mass flow rate is limited to predetermined values ​​allowing the restoration of the torque within a predetermined maximum duration.

[0041] For example, the reduction of the air mass flow rate is achieved by closing a throttle body of the engine.

[0042] According to another characteristic, the second torque value is calculated by the computer using a network of curves linking the torque values ​​to the EGR rates.

[0043] For example, the motor torque setpoint is equal to the second torque value.

[0044] Advantageously, when the current torque supplied by the engine reaches the second torque value, the computer performs a reduction in ignition advance allowing the engine to produce the target torque necessary for changing gear ratio.

[0045] Advantageously, if no second torque value has been found to enable the target torque to be reached by simply withdrawing the advance, the computer sets a zero EGR setpoint and controls the reduction of the EGR rate by closing an EGR valve.

[0046] According to an advantageous characteristic, during the decrease of the EGR rate towards the set value, the computer evaluates at high frequency the minimum torque achievable only by withdrawal of advance.

[0047] Advantageously, the computer proceeds with the necessary advance withdrawal to obtain the target torque necessary for changing gear ratio.

[0048] The invention also relates to a system for controlling the torque delivered during a gear change by an internal combustion engine of a motor vehicle equipped with at least one system for partial recirculation of exhaust gases at the intake.

[0049] The torque control system comprises means for determining a target torque value required for changing gear ratios, means for determining a first torque value that the engine can produce, from its current operating point, by removing the ignition advance, and means for determining a second torque value, lower than the current torque of the engine, from which it is possible to produce the target torque value by resorting only to removing the ignition advance of the engine. Brief description of the drawings

[0050] 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:

[0051] [Fig. 1], [Fig.2] and [Fig.3], which have already been mentioned, illustrate respectively the pressure-volume diagram of a cylinder of a four-stroke internal combustion engine of a motor vehicle according to a conventional cycle, the combustion duration as a function of the EGR rate present in the combustion chamber, and the possible variation ranges of the ignition advance as a function of the EGR rates.

[0052] [Fig.4] illustrates, schematically, the structure of a combustion engine internal of a motor vehicle equipped with a torque control system according to the invention; and

[0053] [Fig.5] illustrates a flowchart of the torque control method, implemented by the control system, according to an embodiment of the invention. Detailed description of at least one embodiment

[0054] In the example illustrated in [Fig.4], the internal combustion engine 6 comprises, in a non-limiting manner, three cylinders 7 in line, a fresh air intake manifold 8, an exhaust manifold 9 and a turbo-compression system or turbocharger 10.

[0055] The cylinders 7 are supplied with air via the intake manifold 8, or intake distributor, itself supplied by a pipe 11 provided with a filter air 12 and turbocharger 10 of engine 6.

[0056] The turbocharger 10 essentially comprises a turbine 10a driven by the exhaust gases and a compressor 10b mounted on the same shaft as the turbine 10a and providing compression of the air distributed by the air filter 12, with the aim of increasing the quantity (mass flow rate) of air admitted into the cylinders 7 of the engine 6 for an identical volume flow rate.

[0057] The turbine 10a 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. Alternatively, the invention may use a turbine 10a with fixed geometry. In the case of the use (not shown) of a turbine 10a with fixed geometry, the quantity of energy taken by the turbine 10a is regulated by adjusting the proportion of the flow rate of the exhaust gases passing through the turbine, using an exhaust discharge valve, mounted on a bypass circuit associated with the turbine 10a.

[0058] The internal combustion engine 6 thus comprises an intake circuit Ca and an exhaust circuit Ce.

[0059] The intake circuit Ca comprises, from upstream to downstream in the direction of air circulation:

[0060] - the air filter 12 or air box;

[0061] - a flow meter 13 arranged in the intake pipe 11 downstream of the air filter 12; the flow meter 13 being configured to measure the actual value of the air flow entering the engine 6;

[0062] - an air intake valve 14;

[0063] - the compressor 10b of the turbocharger 10 configured to compress the fresh gases intake and low pressure recirculated exhaust gases, as will be described later;

[0064] - a throttle body 15 or a gas intake valve in the engine;

[0065] - a heat exchanger 16 configured to cool the intake gases cor corresponding to a mixture of fresh air and recirculated gases after their compression in the compressor 10b; and

[0066] - the intake manifold 8.

[0067] The compressor is associated with a bypass circuit equipped with an inlet discharge valve 17 which opens in the event of sudden closure of the throttle body 15, to prevent the compressed air, located between the compressor 10b and the throttle body 15, from passing through the compressor 10b and damaging it, when, for example, the driver of the vehicle suddenly lifts his foot off the accelerator pedal.

[0068] The exhaust circuit Ce comprises, from upstream to downstream in the direction of circulation of the burnt gases:

[0069] - the exhaust manifold 9;

[0070] - the turbine 10a of the turbocharger 10 configured to take energy from the exhaust gases passing through the turbine, the expansion energy being transmitted to the compressor 10b via the common shaft, for the compression of the intake gases; and

[0071] - a system 18 for depolluting the combustion gases of the engine.

[0072] As regards the exhaust manifold 9, the latter recovers the exhaust gases resulting from the combustion and evacuates them to the outside, via a gas exhaust duct 19 opening onto the turbine 10a of the turbocharger 10 and via an exhaust line 20 mounted downstream of the turbine 10a.

[0073] The engine 6 further comprises a partial recirculation circuit 21 of the exhaust gases at the intake, called the “EGR” circuit (“exhaust gas recirculation” in English terms).

[0074] This circuit 21 is here, in a non-limiting manner, a low-pressure exhaust gas recirculation circuit, called “EGR BP”. It is connected to the exhaust line 20, downstream of said turbine 10a, and in particular downstream of the gas depollution system 18, and returns the exhaust gases to the fresh air supply pipe 11, upstream of the compressor 10b of the turbocharger 10, in particular downstream of the flow meter 13. The flow meter 13 only measures the flow of fresh air alone.

[0075] As illustrated, this recirculation circuit 21 comprises, in the direction of circulation of the recycled gases, a cooler 21a, a filter 21b, and a “V EGR BP” valve 21c configured to regulate the flow rate of the recycled low-pressure exhaust gases to the engine intake. The “V EGR BP” valve 21c is arranged downstream of the cooler 21a and the filter 21b and upstream of the compressor 10b.

[0076] It will be noted that the air intake valve 14 can also be used to force the circulation of a flow of low-pressure exhaust gases in the BP EGR circuit in the case where the vacuum between the exhaust circuit and the intake circuit is insufficient. In this case, closing the valve 14 would create a vacuum downstream, capable of sucking gases from the BP EGR circuit.

[0077] The system 18 for depolluting the combustion gases of the engine comprises a first post-treatment device 22 comprising two three-way catalysts 22a, 22b in series which can be electrically heated, with at least one first oxygen sensor 23 mounted upstream of the first post-treatment device 22.

[0078] The first upstream oxygen sensor 23 is generally used to regulate in a closed loop the value of the richness of the air-fuel mixture in the engine around a set value, for example the value 1 corresponding to an air-fuel mixture in the stoichiometric proportions.

[0079] Furthermore, a second optional oxygen sensor 24, for example of the binary or proportional type, can be mounted downstream of the first post-treatment device so as to be able to correct the setpoint value of the richness regulation loop, in particular with the aim of adjusting the quantity of oxygen stored inside the first depollution device 22.

[0080] The gas depollution system 18 further comprises a second post-treatment device 25 which is here a fine particle filter, and a third post-treatment device 26, for example a three-way catalyst. It may also comprise a third oxygen probe 27, for example of the binary type, mounted downstream of the second device 25, for example for diagnostic purposes.

[0081] The engine 6 is associated with a fuel circuit comprising, for example, fuel injectors (not referenced) injecting gasoline directly into each cylinder 7 from a fuel tank (not shown).

[0082] Furthermore, the engine 6 comprises a computer 28 configured to control the various elements of the internal combustion engine from data collected by sensors at different locations in the engine.

[0083] The calculator 28 comprises a calculation module 29, a measurement module 30 and a control module 31.

[0084] In the spark-ignition engine, the engine speed-load operating point is adjusted by the engine computer 28 by adjusting in particular a quantity of air, a quantity of exhaust gases recycled to the BP EGR intake, and a quantity of fuel. By "quantity" is meant here a mass flow rate.

[0085] A method 40 for controlling the torque provided by a conventional cycle internal combustion engine as described above will now be described with reference to [Fig. 5]. The method 40 makes it possible to control the value of the torque produced by the engine, to achieve the values ​​necessary for changing gears in the gearbox.

[0086] Gearbox gear changes can be initiated by the computer 28 or by the driver, for example by operating a gear lever.

[0087] For example, in the case of an automated gearbox which makes the gear change decisions independently of the driver's wishes, a strategy implemented by the computer 28 may consist of modifying the gear ratio at an operating point of the engine having a torque different from the current torque, in order to reduce the specific consumption of the engine at equal power.

[0088] In a first step 41, the computer 28 detects that it is going to engage such a gear change and requests the gearbox control system to obtain the value not to be exceeded of the torque C_target, necessary for the gearbox during the gear change.

[0089] The value of C_target may be substantially zero if the engine alone produces the torque transmitted to the input shaft of the gearbox. Alternatively, it may be a slightly higher value when the engine is mounted in a hybrid-powered vehicle in association with an electric machine that provides negative torque to the input shaft of the gearbox to compensate for the torque of the thermal engine. Such a hybrid powertrain device is for example disclosed in publication FR3022495-A1.

[0090] In the following step 42, the computer 28 determines the minimum value of the torque C_retrait that the engine can produce by making advance withdrawals from its current operating point and without creating combustion instability. An operating point of the engine 6 is characterized by a current torque provided by the engine using a certain air flow rate, a certain EGR rate and the optimal ignition advance. For a given EGR rate, the torque C_retrait corresponds to the combustion stability limit as represented by the low threshold of the corresponding curve in [Fig. 3], the peak of which corresponds to the current torque obtained with the optimal ignition advance.

[0091] During the following step 43, the calculator 28 checks whether the value of the torque C_target determined in step 41 is less than the value of the torque C_withdrawal determined in step 42.

[0092] If this is not the case, then it is not necessary to reduce the EGR rate, nor to modify the position of the throttle body and the computer 28 only proceeds to remove the ignition advance necessary to obtain the torque C_target without creating combustion instability (step 44).

[0093] If the value of the torque C_target determined in step 41 is lower than the value of the torque C_withdrawal determined in step 42, the computer 28 determines, during the following step 45, a value of torque C_intermediate, lower than the current torque, to be obtained by reducing the quantity of air admitted (for example by closing the throttle body) and for which it would be possible to obtain the torque C_target by withdrawal of advance only. The quantity of air is understood as a mass flow rate. The computer 28 limits the drop in the mass flow rate of air to predetermined values ​​which allow the restoration of the torque after the change of gear ratio to take place within a predetermined maximum duration. The value of the torque C_intermediate, if it exists, is determined by the computer 28 based on a network of curves such as those of [Fig.3], pre-programmed and contained in its memory, linking the different torque values ​​for the constant EGR rate of the current torque.

[0094] During the following step 46, the computer 28 checks whether such a torque value C_intermediate was found in step 45.

[0095] If this is the case, during the following step 47, the computer 28 assigns the value C_intermediate to the torque setpoint and proceeds to reduce the air flow, in particular by closing the throttle body.

[0096] After obtaining the torque C_intermediate in step 47, the computer 28 performs the ignition advance removal which makes it possible to obtain the torque C_target (step 48).

[0097] After the gear ratio change has been carried out, the computer 28 restores the torque to the value C_intermediate, by adjusting the previous ignition advance value, then increases the air flow in particular by reopening the throttle body to obtain the torque value before the gear ratio change.

[0098] During the following step 49, if no torque value C_intermediate has been found in step 45, the computer 28 sets a zero EGR rate setpoint and commands the closing of the EGR valve 21c (step 49a). The effective drop in the EGR rate to a zero value lasts between 200ms and 1000ms depending on the engine flow rate and the intake EGR volume. For a large part, this time corresponds to the gearbox preparation time including, for example, the engagement of the next gear or the slipping of the clutches. During this drop in the EGR rate, the computer 28 re-evaluates at high frequency the minimum torque achievable by the advance withdrawal alone as a function of the new EGR rate (step 49b).

[0099] For example, the computer 28 determines, after the start of the closing of the EGR valve, a value of the rate of EGR actually entering the cylinders. The value of the flow rate passing through the EGR valve is calculated from a Barré de Saint-Venant equation, a delay time applied to take into account the distance between the EGR valve 21c and the cylinders 7 and an engine filling model from the relationship:

[0100] = 120 (1) NX Cylinder capacity X TP“*R

[0101] In which:

[0102] ^rdvl denotes the volumetric yield or “filling”, dimensionless;

[0103] Qmot denotes the total mass flow rate actually entering, in kg / s;

[0104] N denotes the speed, in rpm;

[0105] Cylinder capacity means the cylinder capacity of the engine, in m3;

[0106] Pcol denotes the pressure in the intake manifold, in Pa;

[0107] Tcol, denotes the temperature in the intake manifold, in K; and

[0108] R denotes the mass constant of ideal gases for air equal to approximately 287.058 J / kg*K •

[0109] In other words, the computer 28 considers that the EGR flow in the engine at a current instant is equal to the flow rate through the valve at a previous instant separated from the current instant by the value of the delay time.

[0110] During the decrease of the EGR rate towards a zero value, the computer 28 proceeds to the removal of the ignition advance necessary to obtain the torque C_target without creating combustion instability (step 49c).

Claims

Claims

1. Method for controlling the torque delivered during a gear ratio change by an internal combustion engine (6) of a motor vehicle equipped with at least one partial recirculation system (21) of the exhaust gases at the engine intake, characterized in that it comprises the following steps: - determining a target torque value (C_target) necessary for the gear ratio change; - determining a first torque value (C_withdrawal) that the engine can produce, from its current operating point, by carrying out ignition advance withdrawals; - determining a second torque value (C_intermediate), lower than the current torque of the engine (6), from which it is possible to produce the target torque value (C_target) by resorting only to an ignition advance withdrawal of the engine (6);said method comprising a step of canceling the EGR rate carried out if no second torque value (C_intermediate) has been found to allow the target torque (C_target) to be reached by simply removing the advance.;

2. Method according to claim 1, in which the second torque value (C_intermediate) is obtained by reducing the mass flow rate of air entering the engine (6).

3. A method according to claim 2, wherein the decrease in the air mass flow rate is limited to predetermined values ​​allowing the restoration of the torque within a predetermined maximum duration.

4. A method according to claim 3, wherein the reduction in the air mass flow rate is achieved by closing the throttle body.

5. Method according to claim 3, in which the second torque value (C_intermediate) is calculated by the computer (28) using a network of curves linking the torque values ​​to the EGR rates.

6. Method according to any one of claims 3 to 5, in which the torque setpoint of the motor (6) is equal to the second torque value (C_intermediate).

7. Method according to claim 6 in which, when the current torque supplied by the engine reaches the second torque value (C_intermediate), the computer performs an ignition advance reduction allowing the engine (6) to produce the target torque (C_target) necessary for the gear ratio change.

8. The method of claim 1, wherein the step of canceling the EGR rate comprises setting a zero EGR setpoint and controlling the decrease in the EGR rate by closing an EGR valve.

9. Method according to claim 8, in which, during the decrease of the EGR rate towards the set value, a computer (28) of the engine (6) evaluates at high frequency the minimum torque achievable only by withdrawal of advance.

10. Method according to claim 9, in which the computer (28) carries out the advance withdrawal necessary to obtain the target torque (C_target) necessary for the gear ratio change.

11. System for controlling the torque delivered during a gear change by a motor vehicle internal combustion engine equipped with at least one exhaust gas recirculation system at the intake, characterized in that it comprises: - means for determining a target torque value (C_target) necessary for the gear change; - means for determining a first torque value (C_withdrawal) that the engine can produce, from its current operating point, by carrying out ignition advance withdrawals; - means for determining a second torque value (C_intermediate), lower than the current torque of the engine (6), from which it is possible to produce the target torque value (C_target) by resorting only to an ignition advance withdrawal of the engine (6); and - means for canceling the EGR rate.

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