EP2761153B1 - Control of the injection of fuel upon combustion engine start-up - Google Patents

Description

Technical field of the invention

The invention relates to the field of the control of fuel injection, especially gasoline, at the start of a heat engine, in particular operated in the context of a motor vehicle.

The subject of the invention is more particularly a fuel injection control method at the start of a heat engine, an electronic control unit implementing this method, and a motor vehicle equipped with such a unit.

State of the art

The growing search for reduction of pollutant emissions leads to the search for consumption gains on the thermal engines and thus to optimize as much as possible all the operating zones of the engine.

The starting phase of the engine is generating consumption and polluting emissions because during this phase, it is necessary to provide a high energy to start the engine. This problem is all the more critical that the exhaust after-treatment system has, at the same time, a low efficiency due to its low temperature. Any fuel not consumed by explosions within the engine is present as HC / CO exhaust.

In a known manner, the control of the injection during the start-up phase of an internal combustion engine exploits an open-loop automation solution and therefore imposes a calibration taking into account the manufacturing, environmental and other dispersions. of fuel type, which impact the engine. The injection is regulated (by a control in opening / closing of the injectors to adjust the injection time) on a lump sum instruction that takes into account these dispersions to increase the richness of the air / fuel mixture. It is necessary to greatly enrich the air / fuel mixture at startup so that this operation is possible whatever the conditions. In particular, the calibration must make it possible to start the most inert motor (i.e. which has the most internal mechanical friction) powered by the least volatile fuel possible. This results in the majority of cases excessive consumption compared to the actual needs of each engine and untreated pollutant emissions by the after-treatment system which usually includes a catalyst and which has not yet reached its operating temperature at start-up.

It is only after the attainment of a sufficient temperature following the start that a closed loop automation control becomes possible. Indeed, before reaching this temperature, the determination of a reliable signal representative of the richness to allow a necessary return to a closed-loop regulation currently remains impossible.

Object of the invention

The object of the present invention is to provide a fuel injection control solution at the start of a heat engine which overcomes the disadvantages listed above.

A first aspect of the invention relates to a method of controlling fuel injection at the start of a heat engine, which comprises a first step of determining a target fuel quantity at startup, according to a difference between motor setpoint acceleration and instantaneous motor acceleration.

The method comprises a second step of injecting a quantity of fuel corresponding selectively to the set target fuel amount at the start determined in the first step or a preset amount of basic target fuel.

The selection from the starting set fuel quantity and the preset basic fuel set quantity depends at least on a first condition using a criterion related to the engine RPM and a second condition using a difference criterion. between a real engine speed derivative and a engine speed derivative setpoint.

The determination step may comprise a first phase for determining a difference between a real engine speed derivative and an engine speed derivative setpoint, the difference between the actual speed derivative and the speed derivative reference being representative. the difference between the setpoint acceleration of the motor and the instantaneous acceleration of the motor.

In the first phase, the actual speed derivative can be determined from a value of the derivative of the instantaneous engine speed of a temperature of a coolant coolant of the engine.

In the first phase, the engine speed derivative setpoint can be determined from the temperature of the engine coolant, the calculation step of said derivative being proportional to the instantaneous speed.

The determination step may comprise a second phase of generating a richness correction factor at startup, from a map taking as input the difference between the derivative of actual speed and the engine speed derivative setpoint and the coolant temperature of the engine cooling.

The mapping can correspond to a proportional regulator of wealth correction.

The determining step may comprise a third phase of characterizing the starting amount of fuel at startup, from the start-up richness correction factor and a preset amount of base set fuel.

The third characterization phase may include a modulation of the start-up richness correction factor as a function of the number of possible engine restarts.

The first condition can be verified for example if the instantaneous engine speed is greater than or equal to a first predetermined threshold.

The second condition can be verified for example if the difference between the real engine speed derivative and the engine speed derivative setpoint is greater than or equal to a second predetermined threshold.

The second step may consist in injecting, during a predetermined period, the quantity of target fuel at the start determined in the first step, when the first and second conditions are simultaneously checked.

The determined duration may be a function of the temperature of the coolant coolant of the engine.

The selection of the starting fuel quantity at the start and the preset amount of base set fuel may depend on the number of possible engine restarts.

The second step may include a regulation of the fuel injection time at the engine according to the amount of fuel to be injected.

A second aspect of the invention relates to an electronic control unit which implements the fuel injection control method at the start of a heat engine as presented above.

A third aspect of the invention relates to a motor vehicle comprising such an electronic control unit, a heat engine, and a fuel injection device supplying the heat engine and controlled by the electronic control unit.

Brief description of the drawings

• la figure 1 illustre le schéma de principe d'un exemple d'unité de commande électronique mettant en oeuvre un procédé de commande selon l'invention,
• la figure 2 illustre la structure du bloc « Facteur_Démarrage » de la figure 1,
• la figure 3 illustre la structure du bloc « Dérivée_Consigne » de la figure 2,
• la figure 4 illustre la structure du bloc « Dérivée_Instantanée » de la figure 2,
• la figure 5 illustre la structure du bloc « Masse_Carburant_Démarrage » de la figure 1,
• la figure 6 illustre la structure du bloc « Mode_Démarrage » de la figure 5,
• la figure 7 illustre la structure du bloc « Application_Masse_Carburant » de la figure 5,
• la figure 8 illustre la structure du bloc « Condition_Desactivation » de la figure 7,
• et la figure 9 représente la courbe d'évolution dans le temps du régime moteur et de la différence entre une accélération de consigne du moteur et une accélération instantanée du moteur, lorsque la commande selon l'invention est appliquée.

Other advantages and features will emerge more clearly from the following description of particular embodiments of the invention given as non-restrictive examples and shown in the accompanying drawings, in which:

• the figure 1 illustrates the block diagram of an example of an electronic control unit implementing a control method according to the invention,
• the figure 2 illustrates the structure of the "Start_Factor" block of the figure 1 ,
• the figure 3 illustrates the structure of the "Derivative_Consign" block of the figure 2 ,
• the figure 4 illustrates the structure of the block "Derivative_Standard" of the figure 2 ,
• the figure 5 illustrates the structure of the block "Start_Fuel_Mass" of the figure 1 ,
• the figure 6 illustrates the structure of the "Mode_Start" block of the figure 5 ,
• the figure 7 illustrates the structure of the block "Application_Mass_Fuel" of the figure 5 ,
• the figure 8 illustrates the structure of the block "Condition_Desactivation" of the figure 7 ,
• and the figure 9 represents the curve of change in the time of the engine speed and the difference between a setpoint acceleration of the engine and an instantaneous acceleration of the engine, when the control according to the invention is applied.

Description of preferred modes of the invention

The solution proposed below, with reference to Figures 1 to 9 relates to the control of the injection of a fuel, for example gasoline, during the start-up operation of a heat engine, for example equipping a vehicle, particularly of the automotive type.

A first aspect thus relates to a method of controlling fuel injection at the start of a heat engine. According to an important characteristic, the method comprises a first step consisting in determining a set amount of fuel at startup, the determination being a function of a difference between a setpoint acceleration of the engine and an instantaneous acceleration of the engine. As will be further detailed subsequently, the control method then comprises a second step of injecting a quantity of fuel "Q_INJ_CONS_DEM" corresponding selectively to the amount of fuel set at startup "Q_INJ_DEM" determined in the first step, or to a preset amount of base set fuel "Q_INJ".

The principle of this command is to compare an acceleration setpoint of the engine and the actual acceleration of the engine. These include angular acceleration. The difference thus obtained is representative of the mechanical torque delivered by the engine and necessary for starting.

The figure 1 illustrates the block diagram of an example of an electronic control unit implementing a control method according to the invention. For this, the control unit comprises a first block of establishment of a wealth correction factor at startup, this first block being named "Start_Factor". This correction factor "Fac_Corr_Richesse" coming out of the first block "Facteur_Démarrage" feeds one of the entries of a second block of setting the quantity of fuel to be injected "Q_INJ_CONS_DEM", this block being named "Masse_Carburant_Start" on the figure 1 .

• température d'un liquide caloporteur de refroidissement du moteur : « Temp_eau »,
• dérivée du régime moteur instantané : « DERV_N »,
• états moteurs : « ETAT_MOT »,
• régime moteur réel : « N »,
• quantité préétablie de carburant de consigne de base : « Q_INJ »,
• évènements sur la mise sous tension de l'unité : « EV_PW »,
• évènements sur le calage du moteur : « EV_STA »,
• évènements sur les points morts hauts : « EV_TDC »,
• évènement périodique, par exemple à une période de 10ms, permettant le calcul de la première étape en discret afin de pouvoir être intégré dans un calculateur moteur : « EV_10ms ».

Subsequently, the rest of the nomenclature between the drawings and the terms of the description is as follows:

• temperature of an engine coolant: "Water temp",
• derivative of the instantaneous engine speed: "DERV_N",
• motor states: "STATUS_MOT",
• actual engine speed: "N",
• preset quantity of basic fuel of reference: "Q_INJ",
• events on turning on the unit: "EV_PW",
• engine stall events: "EV_STA",
• events on the top dead spots: "EV_TDC",
• periodic event, for example at a period of 10ms, allowing the calculation of the first step in discrete so as to be integrated in a motor ECU: "EV_10ms".

In order to compare the motor acceleration setpoint and the actual motor acceleration, the determination step comprises a first phase of determining a difference between a real engine speed derivative (output 1 called "instantaneous derivative" on the figure 4 ) and an engine speed derivative setpoint (output 1 called "Setpoint derivative" on the figure 3 ), the difference between the real speed derivative and the speed derivative setpoint being representative of the difference between the engine setpoint acceleration and the instantaneous engine acceleration.

• On pose : $$E=\frac{1}{2}I{\mathrm{<figure-callout\; id="2"\; label="\omega "\; filenames="imgf0005.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^2\mathrm{et}P=C\omega \mathrm{et}\frac{\mathit{dE}}{\mathit{dt}}=P$$
  

Avec

• E : l'énergie
• I : le moment d'inertie
• ω : le régime moteur
• P : la puissance
• C : le couple

The reasoning is as follows:

• We pose: $$E=\frac{1}{2}I{\mathrm{<figure-callout\; id="2"\; label="\omega "\; filenames="imgf0005.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^2\mathrm{and}P=\mathrm{VS}\omega \mathrm{and}\frac{\mathit{of}}{\mathit{dt}}=P$$
  

With

• E: energy
• I: the moment of inertia
• ω: the engine speed
• P: the power
• C: the couple

For the derivative setpoint, we deduce: $$\frac{{\mathit{of}}_{\mathit{sp}}}{\mathit{dt}}={\mathrm{VS}}_{\mathit{sp}}{\omega }_{\mathit{sp}}\Rightarrow \frac{E_{\mathit{sp}}-E_{\mathit{sp}\left(i-1\right)}}{\mathit{dt}}={\mathrm{VS}}_{\mathit{sp}}{\omega }_{\mathit{sp}}$$

ω _sp étant fonction de « dt », le passage en discret donne $$\frac{{\omega }_{\mathit{sp}}-{\omega }_{\mathit{sp}\left(i-1\right)}}{\mathit{dt}}=\frac{{\mathit{d\omega }}_{\mathit{sp}}}{\mathit{dt}}=C_{\mathit{sp}}$$

For the rest of the reasoning, the moment of inertia and the constant, identical to the two accelerations or energies, are neglected. $$\frac{E_{\mathit{sp}}-E_{\mathit{sp}\left(i-1\right)}}{{\omega }_{\mathit{sp}}\times \mathit{dt}}={\mathrm{VS}}_{\mathit{sp}}=\frac{{{\mathrm{<figure-callout\; id="2"\; label="\omega "\; filenames="imgf0005.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^2}_{\mathit{sp}}-{{\mathrm{<figure-callout\; id="2"\; label="\omega "\; filenames="imgf0005.png"\; state="\{\{state\}\}">\omega </figure-callout>}}^2}_{\mathit{sp}\left(i-1\right)}}{{\omega }_{\mathit{sp}}\times \mathit{dt}}$$

ω _sp being a function of "dt", the passage in discrete gives $$\frac{{\omega }_{\mathit{sp}}-{\omega }_{\mathit{sp}\left(i-1\right)}}{\mathit{dt}}=\frac{{\mathit{d\omega }}_{\mathit{sp}}}{\mathit{dt}}={\mathrm{VS}}_{\mathit{sp}}$$

With identical reasoning for the instantaneous couple, we have $${\mathrm{VS}}_i=\frac{d{\omega }_i}{\mathit{dt}}$$

The difference between the two derivatives (setpoint and instantaneous) gives an image of the torque needed to reach the setpoint as a function of the instantaneous speed.

So, the figure 2 illustrates the structure of the "Start_Factor" block of the figure 1 , which consists on the one hand of a block "Dérivée_Consigne" detailed in figure 3 and on the other hand a block "Derivative_Standard" detailed in the figure 4 . The block "INSTANT_DRIVE" determines the derivative of real engine speed, corresponding to the output signal 1 called "instant derivative" on the figure 4 . The "Derivative_Consigne" block determines the engine speed derivative setpoint, corresponding to the output signal 1 called "Setpoint derivative" on the figure 3 .

In the first phase and with reference to figure 4 , the real-regime derivative (output 1 called "Filtered Diet Derivative" on the figure 4 ) is determined from a value of the derivative of the instantaneous engine speed (input called "DERV_N") and a temperature of a coolant coolant of the engine (input called "Water Temp").

qui n'est pas représentée. Ce calcul est effectué au PMH (par l'intermédiaire du paramètre « EV_TDC ») pour être cohérent avec le calcul de la consigne de dérivée de régime moteur (sortie 1 appelée « Dérivée de consigne » sur la figure 3).The setpoint derivative is constructed in the form: $$\mathit{N\_grad}=\frac{\mathrm{NOT}\cdot \left(\mathrm{NOT}-{\mathrm{NOT}}_{i-1}\right)}{120}\times {\mathrm{NOT}}_{\mathit{cyl}}$$

who is not represented. This calculation is performed at the PMH (via the parameter "EV_TDC") to be consistent with the calculation of the engine speed derivative setpoint (output 1 called "Setpoint derivative" on the figure 3 ).

permet de filtrer la dérivée afin d'éliminer le bruit. Le facteur « k » dépend de « Temp_eau » grâce au bloc « Gain_fct_Temperature_Eau ». Une saturation « Saturation » entre une valeur maximum et une valeur minimum permet en outre d'éviter les excursions trop importantes de la dérivée.A first order filter "Filter ^1st order" type $${\mathit{DervN}}_{\mathit{filtered}}=k\cdot {\mathit{DervN}}_{\mathit{brute}}+\left(1-k\right)\cdot {\mathit{DervN}}_{\mathit{filtered}}-1$$

allows filtering the derivative to eliminate noise. The factor "k" depends on "Temp_eau" thanks to the block "Gain_fct_Temperature_Eau". A "saturation" saturation between a maximum value and a minimum value also makes it possible to avoid excessive excursions of the derivative.

On the other hand in the first phase and with reference to the figure 3 , the engine speed derivative setpoint (output 1 called "Setpoint derivative" on the figure 3 ) is determined from the engine coolant temperature ("Water Temp"). The calculation step of said derivative is proportional to the instantaneous speed "N", thanks for example to the "Event ()" input of the "Start_Factor" block at the figure 1 .

et permet d'éliminer le bruit. Le facteur « k » dépend de « Temp_eau » grâce au bloc « Gain_fct_Temperature_Eau » sur la figure 3.Specifically, the structure "Derivative_Consign" calculates the derivative at each Top Dead Center "EV_TDC" and during initializations at power-up "EV _PW" and engine timing "EV_STA". Thus the calculation is consistent with the calculation of the filtered regime derivative in relation to the figure 4 . The derivative setpoint, also called setpoint derivative, is a function of the calculation step, the latter being a function of the "N" regime. We are left with an image of the power needed to start. The operation thus obtained is a derivative setpoint "Derivative setpoint" which varies according to the instantaneous regime "N" and tends to decrease as the speed increases. Saturation saturation as well as a first-order filter allow a coherence vis-à-vis the calculation of the derivative of filtered regime in relation with the figure 4 . This filter is of the type $${\mathit{DervN}}_{\mathit{filtered}}=k\cdot {\mathit{DervN}}_{\mathit{brute}}+\left(1-k\right)\cdot {\mathit{DervN}}_{\mathit{filtered}}-1$$

and helps eliminate noise. The factor "k" depends on "Temp_eau" thanks to the block "Gain_fct_Temperature_Eau" on the figure 3 .

The determination step comprises a second phase of elaboration of the start-up correction factor "Fac_Corr_Richesse", starting from a mapping (block "Fact_enrichissement" on the figure 2 ) taking as input "VAR_X" the difference between the real-regime derivative and the derivative setpoint of engine speed, and the temperature of the engine coolant coolant "TCO" at the input "VAR_Y". In particular, the mapping corresponds to a proportional regulator of wealth correction.

Indeed, as the difference between the motor acceleration setpoint and the actual motor acceleration is not directly transferable for a heat engine, it becomes the input of a proportional correction on the wealth. Thus the correction made during starting is important at low speeds and weakens or even becomes negative during the rise if the actual angular acceleration of the engine exceeds the set point (which may be the case for a very little inert motor ).

In addition and with reference to figure 5 , the determining step comprises a third phase of characterizing the target fuel quantity at start "Q_INJ_DEM", from the start-up correction factor "Fac_Corr_Richesse" and a preset quantity of basic set fuel "Q_INJ". This characterization phase is carried out periodically, for example from the event "EV_10ms".

However, the quantity "Q_INJ" is not directly multiplied by the gain "Fac_Corr_Richesse" coming out of the block "Facteur_Démarrage" and entering the block "Masse_Carburant_Start". On the contrary, the third characterization phase comprises a modulation of the start-up correction factor "Fac_Corr_Richesse" as a function of the number of possible restartings of the engine. This modulation carried out in the block "Mode_Start" depends on the entry "Red_Mot"; this variable comes from a calculation that is not represented.

The block "Mode_Start" is detailed in figure 6 . The "Red_Mot" parameter is used to provide a modulation to the parameter "Fac_Corr_Richesse" in order to establish a final enrichment factor taking into account a notion of difference in the moment of inertia and friction at startup between a situation of first start and a re-start situation. It is this final enrichment factor that is multiplied by the quantity "Q_INJ" to obtain the parameter "Q_INJ_DEM".

In other words, the "Red_Mot" parameter makes it possible to detect possible successive starts. Indeed, during a first start, the oil film is not established, causing greater friction. This first start requires a higher torque, so a larger amount of fuel. Fixes are applied via this detection for re-starts in the "Start_Start" and "Application_Fabric_Mass" blocks.

More precisely, the block "Mode_Start" allows consolidation of the wealth correction factor "Fac_Corr_Richesse". A gain makes it possible to correct this factor during re-starts, then the factor is limited by a saturation in order to avoid aberrant factors to finally be multiplied by the quantity "Q_INJ". This is calculated from the estimation of the air flow entering the engine and the stoichiometry as well as various corrections if necessary.

This control principle makes it possible to provide the heat engine with the right amount of fuel required for starting, thanks to the variable modulation over time conferred by the start-up richness correction factor thus produced.

The order also includes, as indicated above and with reference to the figure 7 , a second step of injecting a quantity of the fuel "Q_INJ_CONS_DEM" corresponding selectively to the quantity of fuel set at the start "Q_INJ_DEM" determined in the first step or the preset quantity of basic fuel setpoint "Q_INJ".

In particular, the method uses the preset quantity of basic set fuel "Q_INJ". This quantity is exploited in a first start-up sequence in combination with the total enrichment factor. Then, once the first sequence has been completed, the method provides a second post-start sequence during which the fuel injection is controlled directly only from the preset quantity of basic set fuel "Q_INJ", regardless of the factor total enrichment.

• une gestion au plus proche du nécessaire de l'injection tout en conservant la prestation de démarrage (robustesse, temps de départ...),
• une prise en compte des dérives et dispersions grâce à cette régulation par exemple proportionnelle,
• une mise au point plus « physique » de l'opération de démarrage (basée sur une richesse de consigne).

From all the foregoing it follows that the control principle makes it possible to introduce a notion of wealth regulation during the start-up phases. Advantages are :

• a management closer to the necessary injection while retaining the start-up benefit (robustness, departure time ...),
• a consideration of the drifts and dispersions thanks to this regulation for example proportional,
• a more "physical" development of the start-up operation (based on a setpoint richness).

This results in a more precise management of the quantities of fuel injected during the start-up phase. Consumption and pollutant emissions are reduced, also allowing potential gains on the precious metal load of the potential catalyst in post-treatment. It should be noted that the proposed solution, although more "physical" and closer to the needs of the engine, remains a proportional regulation in open loop. The accuracy of the richness obtained with respect to the setpoint richness depends very much on the basic setting of the engine, especially the filling.

With reference to the figure 8 , the selection from the set fuel quantity at start "Q_INJ_DEM" and the preset quantity of base set fuel "Q_INJ", depends at least on a first condition using a criterion associated with the instantaneous engine speed "N" and a second condition exploiting a criterion associated with the difference "Diff_Cons / Inst" (corresponding to the output marked 2 on the figure 2 ) between the actual engine speed derivative of the filtered engine and the engine speed derivative setpoint. This selection is made periodically, for example from the event "EV_10ms".

For example, the first condition is verified if the instantaneous speed "N" of the motor is greater than or equal to a first predetermined threshold, for example equal to 1000rpm. On the other hand, the second condition is for example verified if the difference between the real engine speed derivative of the filtered engine and the engine speed derivative setpoint is greater than or equal to a second predetermined threshold, for example equal to 0.

The second step may in particular consist in injecting, for a determined duration Δ ( figure 9 ), the quantity of fuel set at startup "Q_INJ_DEM" determined in the first step, when the first and second conditions are simultaneously checked. The determined duration is a function, for example, of the temperature of the engine coolant coolant "Water Temp" (input 7 of the "Reset_condition" block).

In addition, the selection from the set fuel quantity at startup "Q_INJ_DEM" and the preset amount of basic fuel setpoint "Q_INJ", depends on the number of possible engine restarts, through the signal "Red_Mot" and incoming (entry 2) in the block "Condition_Deseactivation" of the figure 7 , detailed in figure 8 . It is also for the verification of the first and second conditions that the engine speed signal "N" (input 6) and the signal corresponding to the difference between the setpoint and instantaneous derivatives (input 4) are addressed at the input of the block " Condition_Deseactivation ».

For its implementation, the second step may include a regulation of the fuel injection time at the engine according to the amount of fuel to be injected "Q_INJ_CONS_DEM".

A second aspect of the invention relates to an electronic control unit which implements the fuel injection control method at the start of a heat engine as developed above. The control unit comprises all the blocks described above.

A third aspect of the invention relates to a motor vehicle comprising an electronic control unit as mentioned above, a heat engine, and a fuel injection device supplying the heat engine and driven by the electronic control unit. .

Finally, the invention relates to a heat engine controlled by a control unit as described above, and a data recording medium readable by the control unit, on which is recorded a computer program comprising means for computer program codes for implementing the phases and / or steps of a control method as mentioned above.

Finally, it relates to a computer program comprising a computer program code means adapted to the realization of the phases and / or steps of a control method as mentioned above, when the program runs on such a control unit. .

On the figure 9 , the control unit (integrated in any computer or adapted automaton) makes it possible to define (curve C1) a starting state (injection of the quantity "Q_INJ_DEM") to the left of the line T and a conventional operating state (injection of the quantity "Q_INJ") to the right of the line T. The start (left part of the curves C1 to C3 with respect to the line marked T) comprises the patch described above with respect to the quantity "Q_INJ" thanks to the total wealth factor itself. even determined by the start-up wealth correction factor.

The curve C2 represents the evolution in time of the engine speed "N", as well as the illustration of the condition 1. The curve C3 illustrating the difference between the derivative setpoint and the real speed derivative represents the acceleration or the energy needed to start the engine. This difference is transformed into a gain on wealth. On the figure 9 , the determined duration of application of the quantity "Q_INJ_DEM" is marked Δ and corresponds to a delay before coming to its end with the application of the quantity "Q_INJ".

The control device mentioned in this document can be adapted to the air control of the engine (via the throttle valve) or to the control of the advance during starting by taking as reference respectively a reference throttle opening and a reference value of the advance instead of the richness 1.

Claims (16)

1. Method for controlling the injection of fuel on starting up a heat engine, comprising a first step of determining a setpoint fuel quantity on start-up ("Q_INJ_DEM"), as a function of a difference between a setpoint acceleration of the engine and an instantaneous acceleration of the engine, and a second step consisting in injecting a quantity of fuel ("Q_INJ_CONS_DEM") corresponding selectively to the setpoint fuel quantity on start-up ("Q_INJ_DEM") determined in the first step or a pre-established basic setpoint fuel quantity ("Q_INJ"), characterized in that the selection from the setpoint fuel quantity on start-up ("Q_INJ_DEM") and the pre-established basic setpoint fuel quantity ("Q_INJ") depends at least on a first condition exploiting a criterion associated with the instantaneous speed ("N") of the engine and a second condition exploiting a criterion associated with the difference between a real speed derivative of the engine and an engine speed derivative setpoint.
2. Method according to Claim 1, characterized in that the first step of determination comprises a first phase of determining a difference between a real engine speed derivative and an engine speed derivative setpoint, the difference between the real speed derivative and the speed derivative setpoint being representative of the difference between the setpoint acceleration of the engine and the instantaneous acceleration of the engine.
3. Method according to Claim 2, characterized in that, in the first phase, the real speed derivative is determined from a value of the instantaneous speed derivative of the engine ("DERV_N") and of a temperature of an engine cooling heat-transfer liquid ("Temp_water").
4. Method according to either of Claims 2 and 3, characterized in that, in the first phase, the engine speed derivative setpoint is determined from the temperature of the engine cooling heat-transfer liquid ("Temp_water"), the computation pitch of said derivative being proportional to the instantaneous speed ("N").
5. Method according to any one of Claims 2 to 4, characterized in that the first step of determination comprises a second phase of generation of a richness correction factor on start-up ("Richness_Corr_Fac"), from a mapping which takes as input the difference between the real speed derivative and the engine speed derivative setpoint and the temperature of the engine cooling heat-transfer liquid ("Temp_water").
6. Method according to Claim 5, characterized in that the mapping corresponds to a richness correction proportional regulator.
7. Method according to either of Claims 5 and 6, characterized in that the first step of determination comprises a third phase of characterizing the setpoint fuel quantity on start-up ("Q_INJ_DEM"), from the richness correction factor on start-up ("Richness_Corr_Fac") and from a pre-established basic setpoint fuel quantity ("Q_INJ").
8. Method according to Claim 7, characterized in that the characterization third phase comprises a modulation of the richness correction factor on start-up ("Richness_Corr_Fac") as a function of the possible number of engine restarts ("Red_Mot").
9. Method according to any one of the preceding claims, characterized in that the first condition is satisfied if the instantaneous speed ("N") of the engine is greater than or equal to a predetermined first threshold.
10. Method according to any one of the preceding claims, characterized in that the second condition is satisfied if the difference between the real speed derivative of the engine and the engine speed derivative setpoint is greater than or equal to a predetermined second threshold.
11. Method according to any one of the preceding claims, characterized in that the second step consists in injecting, for a determined duration, the setpoint fuel quantity on start-up ("Q_INJ_DEM") determined in the first step, when the first and second conditions are simultaneously satisfied.
12. Method according to Claim 11, characterized in that the determined time is a function of the temperature of the engine cooling heat-transfer liquid ("Temp_water").
13. Method according to any one of the preceding claims, characterized in that the selection from the setpoint fuel quantity on start-up ("Q_INJ_DEM") and the pre-established basic setpoint fuel quantity ("Q_INJ") depends on the possible number of engine restarts ("Red_Mot").
14. Method according to any one of the preceding claims, characterized in that the second step comprises a regulation of the fuel injection time on the engine as a function of the quantity of fuel to be injected ("Q_INJ_CONS_DEM").
15. Electronic control unit which implements the method for controlling the injection of fuel on starting up a heat engine according to one of the preceding claims.
16. Motor vehicle comprising an electronic control unit according to Claim 15, a heat engine, and a fuel injection device supplying the heat engine and driven by the electronic control unit.

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