FR2995025A1 - CONTROL OF THERMAL MOTOR USING FUEL QUALITY INDEX POWERING THE HEAT ENGINE - Google Patents

Abstract

The evaluation of the quality of a fuel supplying a heat engine comprises, at the start of the engine, a follow-up of the variations of the value taken, during a period of analysis, by at least one representative quantity of the mechanical torque delivered and / or deliver by the engine, and an elaboration, from the data obtained at the follow-up, of a fuel quality index. A qualitative qualification of a physical characteristic associated with the fuel is implemented, based on the fuel quality index developed at the production stage, in particular using predetermined qualitative criteria of said physical characteristic.

Description

FIELD OF THE INVENTION The invention relates to a method for evaluating the quality of a fuel supplying a heat engine. The subject of the invention is also a method for controlling the heat engine which comprises a phase during which the evaluation method is implemented, as well as a control unit implementing one of the methods and a vehicle. automobile comprising such a control unit. STATE OF THE ART It is known that internal combustion engines generate polluting exhaust gases. To meet increasingly stringent certification standards, exhaust aftertreatment devices from the engine are fitted to the power train along the exhaust line. Different strategies exist for the control of the engine and the after-treatment devices, for example relating to fuel injection parameters (ignition advance, fuel quantity, fuel / air mixture richness, pre-injection and / or post-injection etc.) or to parameters associated with the motor (speed setpoint, mechanical torque setpoint to be delivered, acceleration setpoint, etc.) and / or to the post-processing device (setting conditions in action, operating temperature etc ...).

These strategies, especially at the start of the engine, are in particular impacted by the quality of the fuel injected into the engine. The fuel plays an important role in the proper functioning of the engine. Its composition influences the quality of combustion. One of the important properties of fuel is its volatility, which is defined in particular by a distillation curve. Figure 6 shows the distillation curves of two different fuels. The percentage of distillation (in the abscissa) at a given temperature (ordinate) between different fuels can have great disparities. For example 100 ° C, a low-volatile fuel (top curve) only has for example about 40% of evaporated compounds while at this same temperature, a more volatile fuel (bottom curve) is for example distilled at 60 ° C. % about.

The distillation curve of a given fuel can be divided into three parts that impact the engine differently: - a head fraction (left side) represents the lightest components of the fuel, ie those that will promote the time and quality the cold start of the engine, - a core fraction (central part) impacts the robustness of the engine operation during takeoffs and transients, - and a tail fraction (right side) which is synonymous with fouling of the engines. Although Figure 6 shows that some fuels adopt a different distillation slope in the core fraction compared to the head fraction.

A current solution to address the issues of fuel volatility is to enrich the mixture between the intake air and the fuel, to ensure an engine start regardless of fuel quality. On the other hand, such a strategy has the effect of penalizing the engine starts and the settings associated with the engine for the most volatile fuels, involving the generation of excess fuel consumption and the emission of pollutants unnecessarily high. Achieving a determination of fuel volatility aims to optimize the settings associated with the engine to minimize fuel consumption and pollution without degrading the approval issued by the engine and the proper operation of the powertrain.

Different strategies already exist to try to quantify the volatility of fuels but are not entirely satisfactory. In particular, they have the disadvantage of being difficult to develop and to be very reproducible.

The document FR-A1-2918712 describes a method of starting an internal combustion engine having means for adapting a quantity of injected fuel according to an estimation of the volatility based on the difference between two engine speed gradients and taking account of the friction torque of the engine.30 FR-A1-2935443 describes a method of adjusting a combustion parameter which is a function of the value of the engine speed, the engine coolant temperature and the engine speed. 'a quality index of engine speed.

EP-A1-1831524 discloses a method for determining the volatility of a fuel to allow the cold start of the engine, which takes into account a percentage of richness and the difference between a predicted value and a measured value. quality at startup.

The document described EP-A1-2037104 discloses a method for recognizing fuel volatility during the post-start step. This method comprises a step of setting a given value of mixture richness corresponding to a given volatility value, a step of calculating the difference between the value of the temporal variation of the angular speed of the crankshaft and a predetermined limit value , and a step of determining the volatility of the fuel as a function of this difference.

US6079396 describes a method estimating fuel volatility as a function of engine speed and adjusting the richness of the air / fuel mixture according to this volatility. OBJECT OF THE INVENTION The object of the present invention is to propose a control solution for a heat engine that overcomes the problems listed above.

In particular, an object of the invention is to provide a solution for evaluating the quality of a fuel supplying the engine that is simple, efficient, reliable, easy to develop and easily reproducible. A first aspect of the invention relates to a method for evaluating the quality of a fuel supplying a heat engine, which comprises: at the start of the engine, a step of monitoring the variations of the value taken, during a period of analyzing, by at least one representative quantity of the mechanical torque delivered and / or to be delivered by the engine, a development step, based on the data obtained at the monitoring stage, of a fuel quality index; a step of qualitatively qualifying a physical characteristic associated with the fuel, based on the fuel quality index developed at the manufacturing stage, in particular using predetermined qualitative criteria of said physical characteristic. The analysis period can begin at a first moment when the engine has a transient peak regime between an initial increase in engine starting speed from a zero engine speed, and an initial decrease in engine speed at startup to a set speed. substantially stabilized idle speed, and stopping at a second time when the difference between the instantaneous engine speed and the idle speed reference speed is less than a predetermined deviation.

The idle setpoint speed may depend on the temperature of a coolant coolant engine. The representative magnitude of the torque delivered by the engine may in particular correspond to the result of a calculation of a gas torque produced by the combustions of a mixture between the intake air and the fuel in the engine cylinders.

The tracking step may comprise a step of calculating the gas torque, based on the following formula: ## EQU1 ## where N is the t = 1 engine speed , a is a calibration parameter, Δt is a weighting coefficient, dt represents the duration of the tth period of an alternating signal representative of the instantaneous engine speed during a "combustion-expansion" phase of an engine cylinder , p is a learning value.

The representative magnitude of the torque to be delivered by the motor can also correspond to the torque required by the motor to reach a torque setpoint as a function of the instantaneous engine speed. Said necessary torque may be equal to the difference between a setpoint acceleration of the motor and an instantaneous acceleration of the motor. The follow-up step may comprise a repetition of the implementation of the following successive steps at different times during the analysis period: determination of a reference value of the engine speed derivative; determination of a speed derivative real engine, - calculation of the difference between the engine speed derivative setpoint and the actual engine speed derivative, this difference being representative of the difference between the motor setpoint acceleration and the instantaneous engine acceleration.

The actual engine speed derivative can be determined from a value of the instantaneous engine speed derivative and the temperature of the engine coolant. The engine speed derivative setpoint can be determined from the temperature of the engine coolant, the step of implementing the engine speed derivative setpoint determining step being proportional to the instantaneous engine speed. .

At the end of each calculation step, the method may comprise a step of determining a target fuel quantity at startup according to the result of the calculation step. The step of determining the amount of fuel set at startup can comprise a step of establishing a wealth correction factor at startup, from a map taking as input the result of the calculation step and the temperature of the coolant coolant of the engine.

The amount of fuel set at startup can be the product between the start-up correction factor and a pre-set amount of base set fuel. At the end of the step of determining the amount of fuel set at startup, the method may comprise a step of injecting a quantity of fuel corresponding to either the preset quantity of basic fuel of reference or the amount of fuel set at startup. The quantity of fuel injected at the injection stage may correspond to: the quantity of fuel set at startup as long as the instantaneous engine speed is less than or equal to a first predetermined threshold and / or if the result of the computation step is less than or equal to a second predetermined threshold; the preset amount of base set fuel otherwise.

The step of developing the fuel quality index may comprise a step of integration over time, over the analysis period, of the value taken by the quantity representative of the mechanical torque delivered and / or to be delivered by engine.

The qualification step includes a step of comparing the fuel quality index developed at the production stage with at least one predetermined threshold. Said at least one predetermined threshold optionally depends on the temperature of the coolant coolant of the engine. The physical characteristic associated with the fuel and qualified at the qualification stage may also correspond to the volatility of the fuel.

The method may comprise: at startup, a step of monitoring the variations of the value taken, during a monitoring period, by a quantity representative of the difference between the setpoint acceleration of the motor and the instantaneous acceleration of the motor; a step of development, from the data from the monitoring step, a startup quality index representative of engine performance during its startup, including an energy efficiency of the engine.

The monitoring period may be prior to the analysis period and correspond to a period separating a first instant when the engine has a zero speed and a second time when the engine reaches the transient peak regime.

The starting quality index may be equal to the ratio between the positive sums and the absolute value of the negative sums of the value taken by the quantity representative of the difference between the setpoint acceleration of the engine and the instantaneous acceleration of the engine.

The method may include a step of weighting the start quality index, based on at least one information representative of a condition of the engine during the monitoring period, including a temperature of the intake air and / or the temperature of the coolant coolant of the engine, and / or a stage of qualification of a chosen starting quality, starting from the index of quality of starting developed, among predetermined qualitative criteria of the starting, and / or a step of characterization, starting from the index of quality of starting, internal mechanical friction of the engine and / or the volatility of the fuel.

The volatility of the fuel can be obtained by an abacus taking as input the starting quality index and the temperature of the coolant coolant of the engine and outputting the volatility of the fuel.

The method may comprise a step of adjusting the result of the qualification step of the physical characteristic associated with the fuel, based on the quality index of starting from the stage of preparation and / or the quality of starting from the stage of qualification of the quality of starting and / or the internal mechanical friction of the engine and / or the volatility of the fuel resulting from the characterization step. A second aspect of the invention relates to a method of controlling the heat engine which comprises a phase during which the evaluation method is implemented and a phase of implementation of a method of driving the engine from data from the evaluation process. The control method may comprise a step of adjusting adjustment parameters associated with the motor, from the qualitative qualification resulting from the qualification step, then a step of applying the adjustments adjusted to said adjustment step, said application step being implemented during a phase of operation of the engine subsequent to said start and / or during a subsequent start of the engine. A third aspect of the invention relates to an electronic control unit which implements the evaluation method and / or the control method.

A fourth aspect of the invention relates to a motor vehicle, comprising a heat engine and such an electronic control unit.

A fifth aspect of the invention relates to a computer-readable data recording medium on which a computer program is recorded comprising computer program code means for implementing the phases and / or steps of such a program. control and / or evaluation method.

Finally, a sixth aspect of the invention relates to a computer program comprising computer program code means adapted to the realization of the phases and / or steps of such a method, when the program is executed by a computer. Other advantages and features will emerge more clearly from the following description of particular embodiments of the invention given by way of non-limiting example and shown in the accompanying drawings, in which: FIGS. 1 to 3 illustrate the different phases and steps of an exemplary control method according to the invention, including a phase of implementation of an exemplary evaluation method according to the invention, - Figure 4 represents the evolution curve in time at the start of an injected amount of fuel (curve C1), an ignition advance (curve C2), a pressure in the manifold (curve C3), the speed motor (curve C4); - FIG. 5 represents the evolution curve in time at the start of an engine speed derivative setpoint (curve C5), of a real engine speed derivative (curve C6), of the difference between the curves C5 and C6 (curve C7), the engine speed (curve C8), a start-up richness correction factor (curve C9), a predetermined amount of basic fuel setpoint (curve C11) ) and a set amount of fuel at start (curve C10), and Figure 6 shows an example of two distillation curves of two fuels.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION In general, the invention makes it possible to achieve and optimize the control of a power unit having a heat engine powered by a fuel, for example gasoline. Essentially, this control described below is used to determine and use a quality of the fuel supplying the engine, which then makes it possible to make adjustments to the engine-related settings and engine control taking into account the quality of the fuel in order to optimizing the fuel consumption, the approval granted by the engine, the speed at which the engine warms up and the exhaust after-treatment devices from the engine, the level of pollution. With reference to FIG. 1, the control method of the heat engine comprises a first phase P1 in the course of which a method for evaluating the quality of the fuel (steps E1 to E9) is implemented and then a second possible phase P2 of implementation of a control method (steps 10 and 11) of the engine from the data from the first phase Pi, ie from the fuel quality evaluation method. The fuel quality evaluation method implemented during the first phase P1 necessarily comprises the steps E6 to E8 described below which make it possible, by means of a fuel quality index, to qualify qualitatively at least one physical characteristic associated with the fuel. On the other hand, the steps E1 to E5 described below are optional but advantageous: they make it possible to evaluate, by means of a quality index of starting, a starting quality of the motor, then possibly to adjust (c ') that is to say modulate, refine, specify), during a step E9 and depending on the start quality, the qualitative qualification of the physical characteristic associated with the fuel determined in step E8. The steps E1-E5 are optionally implemented at least partially prior to the implementation of steps E6 and following. Furthermore, the powertrain control method implemented during the second optional second phase P2 comprises a step El 0 adjustment adjustment parameters associated with the engine, from the qualitative qualification of the fuel from the qualification stage E8 (this qualification of fuel quality possibly being adjusted to the adjustment step E9), then an application step El 1 adjustments adjusted to this step El 0 adjustment. The application stage El 1 is implemented during a phase of operation of the engine subsequent to starting and / or when the engine is subsequently started, which ultimately makes it possible to control the motor as a function of the physical characteristic (in particular the volatility) associated with the qualitatively qualified fuel in step E8. In particular, the adjustment parameters adjusted to the adjustment step El 0 comprise the richness of the mixture between the air and the fuel supplying the heat engine to make the combustions robust and / or to improve the following starts of the engine. motor setpoint, a value of the ignition advance. For example, the qualified quality of the fuel, possibly adjusted to the step E9 as a function of the start quality and / or the boot quality index, for example, finally makes it possible to adjust the step El 0 of the adjustments associated with the engine in a way that ensures optimal engine operation with the right amount of fuel required, depending on fuel quality, especially from its volatility. Indeed, the physical characteristic associated with the fuel that is qualified qualitatively in the qualification stage E8 will correspond in particular (but not exclusively) to the volatility of the fuel.

The percentage of alcohol in the fuel can also be characterized by applying the principle above. Indeed, the introduction of alcohol (ethanol) into the fuel modifies its properties, especially its volatility. Using the strategy with other types of fuel such as, for example, "NGV" (for "Natural Gas Vehicle") could be used to determine the lower heating value.

With reference to FIG. 1, according to an essential characteristic, the method of evaluating the quality of the fuel supplying the heat engine comprises: at the engine start, a step E6 of monitoring the variations in the value taken, during a period of TA analysis (FIG. 4), by at least one representative magnitude of the mechanical torque delivered and / or to be delivered by the engine, - a step E7 of elaboration, from the data obtained at the monitoring step E6, a fuel quality index; - a qualitative qualification step E8 of a physical characteristic associated with the fuel, based on the fuel quality index developed at the production stage. As illustrated in FIG. 1, the transition from the monitoring step E6 to the preparation step E7 may optionally be conditioned to the verification of a condition marked C2. The nature of the condition C2 and the nature of its verification depends, for example, on the type of quantity representative of the mechanical torque delivered and / or to be delivered by the motor and / or on a time data item related in particular to the analysis period TA.

By way of example, the condition C2 is verified (allowing the passage to the step E7 of elaboration) as soon as one arrives at the end of the analysis period TA. However, it can be envisaged that the step E7 of elaboration can be carried out at least partially at the same time as the step E6 of tracking, the data resulting from the step E6 of tracking being then used by a dedicated control unit the operations described later as step E6 monitoring to achieve step E7 development as monitoring step E6 takes place. Although this is not limiting, the analysis period TA may begin at a first moment noted "t2" (FIGS. 4 and 5) in which the heat engine has a transient peak regime (vertex of the curves C4 and C8) between a initial increase in starting speed from a zero engine speed (before start), and an initial decrease in engine speed at start from the transient peak speed to a substantially stabilized idle speed. The idle setpoint speed optionally depends on the temperature of a coolant coolant engine. The analysis period TA then stops at a second instant noted "t3" (FIG. 4) in which the difference between the instantaneous speed (curves C4 and C8) of the engine and the idle setpoint speed is less than a predetermined difference . In other words, the analysis period TA ends when the instantaneous real speed of the engine reaches a threshold equal to the sum between the idle setpoint speed and an offset. This analysis period TA is particularly suitable for carrying out the evaluation method detailed below. Condition C2 may correspond to the crossing of this engine speed threshold. In the analysis period TA, the heat engine after its cold start has not yet reached its optimum operating temperature. The oil film begins to establish, thus reducing the internal friction, the advance (curve C2) and the manifold pressure (C3) are stable and the injection setpoint (curve C1) is also stable. Thus, only the quality of the fuel will influence the value of the negative slope of the regime between instants t2 and t3: a highly volatile fuel will generate good combustions with a strong release of energy and the regime will have a weak slope, while Conversely, a low-volatility fuel will tend to make poor combustions, or even misfires, resulting in a steep decline in the regime over the TA analysis period. In a first embodiment of the evaluation method, the magnitude representative of the torque delivered by the motor may correspond to the result of a calculation of a gas torque produced by the combustions of a mixture between the air of intake and fuel in the engine cylinders. In this particular case, the monitoring step E6 comprises a step E61 for calculating the gas torque, from the following formula: ## EQU1 ## Where N is the speed of the motor, a is a calibration parameter, Δt is a weighting coefficient, dt represents the duration of the tth period of an alternating signal representative of the instantaneous engine speed during a phase of " combustion-expansion "of a motor cylinder, p is a learning value. For example, the calculation step E61 can be performed using a torque measuring device as described in FR-A1-2757945, FR-A1-2818740 and FR-A1-2735232. In a second embodiment, which can be applied independently or in combination with the first embodiment, depending on the nature of the fuel quality index and the number of quantities to be followed for its production, the representative magnitude the torque to be delivered by the motor may correspond to the torque required by the motor to reach a torque setpoint as a function of the instantaneous engine speed. In this second embodiment, the necessary torque is equal to the difference between a setpoint acceleration of the motor and an instantaneous acceleration of the motor, this difference between the instantaneous and setpoint accelerations being determined in steps E62, E63 and E64 described below. . Then, step E7 of developing the fuel quality index may comprise a step E71 of integration over time, over the analysis period TA, of the value taken by said at least one representative quantity of the torque. mechanical delivered and / or delivered by the engine. However, the manner of constructing the fuel quality index may vary depending on the nature of the magnitude whose variations are followed in step E6.

As illustrated in FIG. 1, the qualification step E8 may then comprise a comparison step E81 between the fuel quality index developed in step E7 and at least one predetermined threshold. Said at least one predetermined threshold may in particular depend on the temperature of the coolant coolant of the engine. Such a threshold may be pre-established from tests carried out with a reference fuel whose physical characteristics are perfectly known. The implementation of the qualification step E8 will be carried out, in particular, using predetermined qualitative criteria of said physical characteristic, in that the qualifying qualification may consist in choosing, according to the fuel quality index derived from of step E7, from a list of predetermined qualifying criteria.

For the implementation of step E8, the predetermined qualitative criteria which make it possible to characterize a quality of the physical characteristic of the fuel depend on the nature of this physical characteristic and may vary according to the desired accuracy of the fuel quality. For example, in the case where the physical characteristic qualified qualitatively in step E8 corresponds to the volatility of the fuel, the qualitative criteria may consist of: - the following set of criteria: volatile, weakly volatile, - the set of criteria following: very volatile, medium volatility, low volatility, - the following set of criteria: very volatile, volatile, medium volatility, low volatility, very low volatility, etc. - Once the fuel quality index has been developed step E7, especially by the implementation of step E71, step E8 may consist, in particular by the implementation of step E81, to compare this fuel quality index with at least a predetermined threshold based on a reference fuel whose volatility is well known. For example, in the case where the predetermined qualitative criteria are only two (for example "volatile" and "weakly volatile"), a single predetermined threshold is sufficient: if the fuel quality index developed is below the predetermined threshold, it can be qualitatively qualified as the volatility of the fuel corresponds to the qualitative criterion "weakly volatile". On the contrary, the volatility of the fuel corresponds to the qualitative criterion "volatile" if the fuel quality index is higher than the predetermined threshold. This reasoning can be adapted according to the number of qualifying criteria: the number of predetermined thresholds necessary for the implementation of step E81 will for example be equal to the number of predetermined qualifying criteria minus one.30 Steps E6 to E8 define a fuel quality index and a qualitative qualification of a physical characteristic associated with the fuel advantageously in a field of operation where the core fraction of the distillation curve (FIG. 6) is predominant, where the detection of the differences in volatilities between the fuels is great. With reference to FIG. 2, as indicated previously with reference to the second embodiment, the monitoring step E6 may comprise a repetition of the implementation of the following successive steps at different times during the analysis period TA: a step E62 for determining an engine speed derivative setpoint; a step E63 for determining a real engine speed derivative; a step E64 for calculating the difference between the engine speed derivative setpoint. and the real engine speed derivative. The result of step E62 for determining the engine speed derivative setpoint, during start-up and therefore in particular during the analysis period TA, is represented according to the curve C5 in FIG. 5. The result of the step E63 for determining the real speed derivative, during startup and therefore in particular during the analysis period TA, is represented according to the curve C6 in FIG. 5. The result of the calculation according to the step E64 is represented by the curve C7 in FIG. 5. The difference C7 calculated in step E64 corresponds to the magnitude representative of the difference between the setpoint acceleration of the motor and the instantaneous acceleration of the engine, the value variations of which are monitored at the same time. step E6 tracking.

The reasoning is indeed the following one: One poses: dE co and - Co) and = P 2 di With E: the energy I the moment of inertia the engine speed P: the power C: e couple For the setpoint of derivative we deduce: di - Np For the rest of the reasoning, the moment of inertia and the constant, identical to the two accelerations or energies, are neglected. 0) 111 X th The function of "dt", the passage in discrete gives dri3 With identical reasoning for the instantaneous couple, we have the difference of the two derivatives (setpoint and instantaneous) gives an image of the necessary torque (to be delivered by the motor) to reach a torque setpoint according to the instantaneous speed (curves C4 and C8).

In a particular embodiment of the method, the real engine speed derivative is determined in step E63 from a value of the derivative of the instantaneous real speed of the engine (corresponding to the curve C4 and C8) and the temperature of the coolant coolant of the engine. Similarly, the engine speed derivative setpoint is determined in step E62 from the temperature of the cooling liquid coolant of the engine, the step of implementation of step E62 may advantageously be proportional to the instantaneous speed of the engine . This step also corresponds to the step of performing steps E62 to E64. It should be noted that this step may alternatively be constant, so that steps E62 to E64 are performed in this particular case repeatedly at a constant frequency. At the end of each calculation step E64, the evaluation method may comprise a step E65 for determining a quantity (curve C1 0) of target fuel at startup as a function of the result of the calculation step E64. The determination step E65 may comprise a step E651 for setting a start-up richness correction factor (curve C9), based on a map stored in the control unit taking as input the result of the step E64 of calculation and the temperature of the coolant coolant of the engine. In this case, the quantity (curve C10) of target fuel at start corresponds to the product between the start correction factor (curve C9) and a predetermined quantity (curve C11) of base set fuel (at richness 1, for example ) pre-recorded in the control unit.

During the step E6 of monitoring, in order to supply the heat engine with fuel in order to achieve its optimized starting from the result of the steps E62 to E65, the evaluation method may comprise a step E66 of injection of a quantity of fuel corresponding to either the predetermined amount (curve C1) of basic fuel setpoint or the quantity (curve C10) of target fuel at startup.

In particular, the step E66 is implemented at the end of the step E65 of determining the amount of fuel setpoint at startup, and therefore after each calculation step E64, following the same step of repeating steps E62 to E65. . More precisely, the quantity of fuel injected at the injection step E66 corresponds to: the quantity of fuel set at startup (curve C10) as long as the instantaneous real speed (curve C4 or C8) of the engine is less than or equal to at a first predetermined threshold and / or if the result of the calculation step E64 is less than or equal to a second predetermined threshold, - the preset quantity of basic reference fuel (curve C1), otherwise. Steps E62 to E66 can be carried out alone or in combination with step E61, depending on the nature of the development at step E7 of the fuel quality index and the magnitude of the variations which are followed at the same time. step E6. Advantageously, but in a nonlimiting manner, the evaluation method may furthermore include with reference to FIG. 1: at start-up, a step El of monitoring the variations of the value taken, during a monitoring period TS (FIG. 5), by a magnitude representative of the difference between the motor setpoint acceleration and the instantaneous motor acceleration, - a step E2 of producing, from the data derived from the monitoring step E1, a quality index starting up representative of engine performance during startup, including an energy efficiency of the engine, in particular over the monitoring period TS.30 As illustrated in FIG. 1, the transition from the monitoring step E1 to the step E2 of development of the index of quality of start can be conditioned to the verification of a condition noted Cl. The nature of the condition Cl and the nature of its verification depends on example of the type of magnitude representative of the difference between the instantaneous acceleration and setpoint and / or a time data related in particular to the monitoring period TS. For example, the condition C1 is verified (allowing the passage to the E2 development stage) as soon as one reaches the end of the monitoring period TS.

However, it can be envisaged that the step E2 of development can be carried out at least partially at the same time as the monitoring step E1, the data from step E1 being used by the control unit as and when as step E1 is carried out, to ensure that step E2 development is implemented as the El step takes place. Although this is not limiting, the monitoring period TS (FIG. 5) may advantageously be prior to the analysis period TA and correspond to a duration separating a first instant noted "tl" (see the beginning of the curve C8). where the engine has the zero speed and the second moment "t2" (top of curves C4 and C8) where the engine reaches the transient peak regime. This monitoring period TS is particularly suitable for implementing the evaluation method with an adjustment using the boot quality index. The condition C1 can correspond to the crossing of the transient peak regime by the instantaneous real speed of the engine. During the monitoring step E1, the steps E61 to E65 can also be implemented in the same way as during the monitoring step E6.

This makes it possible to achieve an optimized fuel injection (by an adaptation of the richness by means of the wealth correction factor at startup, in function, in real time, of the torque necessary for the engine to reach its torque setpoint) not only during the setting implementation of the monitoring step E6 over the analysis period TA but also during the implementation of the monitoring step E1 over the monitoring period TS. In a particular embodiment of the evaluation method, the starting quality index developed in the development stage E2 is equal to the ratio between the positive sums and the absolute value of the negative sums of the value taken by the magnitude. representative of the difference between the motor setpoint acceleration and the instantaneous motor acceleration, during the TS monitoring period. It is therefore in particular to follow the evolutions of the curve C7 during the monitoring period TS For this reason, with reference to FIG. 3, the evaluation method can comprise three steps E21, E22 and E23 constituting step E2. In particular: the step E21 corresponds to the determination of the positive sums of the value taken during TS by the quantity representative of the difference between the setpoint acceleration and the instantaneous acceleration, the step E22 corresponds to the determination of the absolute value of the negative sums of the value taken during TS by the quantity representative of the difference between the setpoint acceleration and the instantaneous acceleration, - the step E23 corresponds to the calculation of the ratio between the positive sums and the absolute value of the sums negative from steps E21 and E22. In order to be able to carry out the steps E21 and E22, the quantity representative of the difference between the setpoint acceleration and the instantaneous acceleration can be obtained by implementing the repetition of the steps E62, E63 and E64 during the monitoring step E1. said quantity then corresponds to the result of the calculation step E64 carried out during the monitoring period TS. Steps E21 and E22 can be simultaneous or successive. By "sum" is meant an integration with time of the value taken by the quantity. The result of step E21 corresponds to the sum of the positive areas (marked "S +") of the surfaces delimited by the curve C7 above the zero value marked Z in FIG. 5. The result of step E22 corresponds to its share to the sum of the negative areas (marked "S-") of the surfaces delimited by the curve C7 below Z. The preparation according to step E2 of the index of starting on the basis of such a ratio between "S +" and the absolute value of "S-" is intended to provide an indication of the quality of starting the engine. Indeed, if the torque applied to the motor to reach its set point during the TS monitoring period is long positive, it means that it is necessary to increase the wealth to be able to start the engine. Conversely, if the torque applied to the motor is negative during the monitoring period TS, it means that the motor is supplying too much energy to reach its torque setpoint. The monitoring according to step E1 and the preparation according to step E2 make it possible to observe this difference between the positive and negative pairs in order to finally differentiate the quality of the starting of the motor and thus possibly to subsequently adapt the settings associated with the motor. , following the TA analysis period. Indeed, above a zero difference marked by Z, the difference between the speed derivative setpoint (C5) and the real speed derivative (C6) is positive (which is indicated by S +), so the engine needs additional energy to reach its torque setpoint, implying an increase in the richness of the air / fuel mixture. On the contrary, below Z, the difference between the speed derivative setpoint (C5) and the real speed derivative (C6) is negative, the motor in this case has too much "accumulated" energy and it is possible to 'impoverish the mixture. This is the reason for the existence of the correction factor according to the curve C9, which makes it possible to provide a quantity of fuel "corrected" by this correction factor, from a fuel quantity according to the curve C1 1 pre-established at wealth equal to one.

It finally results that if the positive sum S + is predominant over the negative sum S-, it means that the engine has spent a lot of energy during its start to the monitoring period and without recovering. The engine then potentially has very high internal friction and / or the volatility of the fuel is then low. Conversely, if the negative sum S- is predominant over the positive sum S +, the engine has achieved a good start, which means that the engine has low internal friction and / or that the fuel is very volatile.

Then, with reference to FIG. 1, the fuel quality evaluation method may comprise, following step E2 of preparing the start quality index and before the implementation of the step Monitoring E6: a step E3 of weighting of the starting quality index resulting from the development step E2, according to at least one piece of information representative of an engine condition during the monitoring period TS, in particular the temperature of the intake air and / or the temperature of the cooling liquid of the engine, and / or a step E4 of qualitative qualification of the starting during the monitoring period TS, this qualification being chosen based on the starting quality index developed in step E2, among predetermined qualitative criteria of the start, and / or a step E5 of characterization, starting from the quality index of start-up developed in step E2, of fro internal engine mechanical and / or fuel volatility during the TS monitoring period. For the implementation of step E4, the predetermined qualitative criteria of a start may vary according to the desired accuracy of the boot quality: - they can be constituted by the following set: good start, bad start, - they can be constituted by the following set: good start, average start, bad start, - they can be constituted by the following set: very good start, good start, average start, bad start, very bad start, - etc .. .

Once the boot quality index has been developed, in particular by implementing step E23, it suffices, for example, to compare this boot quality index with at least one predetermined threshold. For example, in the case where the predetermined qualifying criteria are only two, only one predetermined threshold is sufficient: if the developed starting quality index is lower than the predetermined threshold, it can be evaluated that the quality of the engine start corresponds to the criterion qualifier "good start". On the contrary, the quality of the start corresponds to the qualifying criterion "bad start" if the index of quality of starting is higher than the predetermined threshold. This reasoning can be adapted according to the number of qualifying criteria: the number of predetermined thresholds necessary for the implementation of step E4 will for example be equal to the number of predetermined qualifying criteria minus one. In step E5, the volatility of the fuel injected into the engine is obtained in particular by an abacus taking as input the starting quality index and the temperature of the coolant coolant of the engine and outputting the volatility of the fuel injected into the engine. the engine during the monitoring period TS. Such an abacus can be pre-established using a reference fuel whose physical properties are well known. Indeed, the interpretation of the start quality index can be the determination of fuel volatility: the quality of the starting depends essentially on the internal friction of the engine and the volatility of the fuel. By using a matrix determining the engine friction as a function of the temperature of the coolant coolant of the engine and established following tests associated with the reference fuel, the index of quality of starting then becomes a representation close to the quality of the fuel , especially its volatility.

As mentioned above, in the case where the phase 131 of the control method, corresponding to the fuel quality evaluation, comprises the steps E1 to E5 to arrive at an estimation of a start quality, the phase 131 comprises step E9 of adjusting the result of step E8 of qualification of the physical characteristic associated with the fuel, from the quality index of starting from step E2 and possibly E3 and / or the quality of starting from stage E4 of qualification of the quality of the starting and / or the internal mechanical friction of the engine and / or the volatility of the fuel resulting from the step E5 of characterization. Steps E1 to E5 define a quality index starting point in an operating range where the top fraction of the fuel distillation curve (Figure 6) is predominant. By coupling the starting quality index developed in step E2 with the fuel quality index developed in step E7, the settings associated with the post-start engine can be refined, taking into account not only the quality heart fraction but also the quality of the top fraction.

Steps E1 to E5 are optional but advantageous: they make it possible to evaluate, by means of the starting quality index developed in step E2, an engine start quality and / or a volatility of the fuel and / or internal friction of the motor during the monitoring period TS. These results relating to the start quality during the monitoring period TS then make it possible to adjust possibly, during a step E9, the qualitative qualification of the physical characteristic associated with the fuel resulting from the step E8. The invention also relates to an electronic control unit which implements the evaluation method and / or the control method, as well as a motor vehicle, comprising a heat engine and this electronic control unit. Finally, it relates to a computer-readable data recording medium on which is recorded a computer program comprising computer program code means for implementing the phases and / or steps of a control method and / or evaluation as defined above and on a computer program comprising computer program code means adapted to the realization of the phases and / or steps of the control and / or evaluation method, when the program is executed by a calculator.

Claims (34)

REVENDICATIONS1. A method for evaluating the quality of a fuel supplying a heat engine, characterized in that it comprises: - at the start of the engine, a step (E6) of monitoring the variations of the value taken, during a period of analysis (TA), by at least one magnitude representative of the mechanical torque delivered and / or to be delivered by the motor, - a step (E7) of production, from the data obtained in the step (E6) of monitoring, a fuel quality index; - a step (E8) of qualitative qualification of a physical characteristic associated with the fuel, based on the fuel quality index developed at the production stage, in particular with the aid of predetermined qualitative criteria of said physical characteristic. 2. Evaluation method according to claim 1, characterized in that the analysis period (TA) starts at a first instant (t2) when the motor has a transient peak regime between an initial increase in starting speed since a zero engine speed, and an initial decrease in engine speed at startup to a substantially stabilized idling speed. 3. Evaluation method according to claim 2, characterized in that the idle setpoint speed depends on the temperature of a coolant coolant of the engine. 4. Evaluation method according to one of claims 2 and 3, characterized in that the analysis period (TA) stops at a second instant (t3) where the difference between the instantaneous regime (C4, C8) of engine and the idle setpoint speed is less than a predetermined deviation. 5. Evaluation method according to one of claims 1 to 4, characterized in that the magnitude representative of the torque delivered by the engine corresponds to the result of a calculation of a gas torque produced by the combustions of a mixture between intake air and fuel in the engine cylinders. 6. Evaluation method according to claim 5, characterized in that the step (E6) of monitoring comprises a step (E61) for calculating the torque tT gas, from the following formula: Cg -a. .dt + /3).N2 where N is the ti engine speed, a is a calibration parameter, At is a weighting coefficient, dt is the duration of the tth period of an instantaneous representative instantaneous AC signal (C4 , C8) of the engine during a "combustion-expansion" phase of a motor cylinder, p is a learning value. 7. Evaluation method according to one of claims 1 to 6, characterized in that the magnitude representative of the torque to be delivered by the motor corresponds to the torque required by the engine to achieve a torque setpoint as a function of the instantaneous speed (C4, C8) of the engine. 8. Evaluation method according to claim 7, characterized in that said necessary torque is equal to the difference between a setpoint acceleration of the engine and an instantaneous acceleration of the engine. 9. Evaluation method according to claim 8, characterized in that the monitoring step (E6) comprises a repetition of the implementation of the following successive steps at different times during the analysis period: determination (E62). ) an engine speed derivative setpoint (C5), determination (E63) of a real engine speed derivative (C6), calculation (E64) of the difference (C7) between the engine speed derivative setpoint ( C5) and the real engine speed derivative (C6), this difference being representative of the difference between the motor setpoint acceleration and the instantaneous motor acceleration. 10. Evaluation method according to claim 9, characterized in that the real engine speed derivative (C6) is determined from a value of the instantaneous engine speed derivative (C4, C8) and the temperature coolant coolant of the engine. 11. Evaluation method according to one of claims 9 and 10, characterized in that the engine speed derivative setpoint (C5) is determined from the engine coolant temperature of the engine, the setting step of the step (E62) for determining the engine speed derivative setpoint (C5) being proportional to the instantaneous speed (C4, C8) of the engine. 12. Evaluation method according to one of claims 9 to 11, characterized in that at the end of each step (E64) calculation, the method comprises a step (E65) for determining a quantity of fuel starting setpoint (C11) according to the result of the calculation step (E64). 13. Evaluation method according to claim 12, characterized in that the step (E65) for determining the starting fuel quantity (C10) comprises a step (E651) for establishing a correction factor. of start-up richness (C9), from a map taking as input the result of the calculation step (E64) and the temperature of the coolant coolant of the engine. Evaluation method according to claim 13, characterized in that the starting fuel quantity (C10) corresponds to the product between the start correction factor (C9) and a preset quantity of basic fuel ( C11). 15. Evaluation method according to claim 14, characterized in that at the end of the step (E65) for determining the starting fuel quantity (C10), the method comprises a step (E66). injecting a quantity of fuel corresponding to either the preset amount of base set fuel (C11) or the starting fuel quantity (C10). 16. The evaluation method as claimed in claim 15, characterized in that the quantity of fuel injected at the injection step (E66) corresponds to: the quantity of fuel set at startup (C10) as long as the (C4, C8) of the engine is less than or equal to a first predetermined threshold and / or if the result of the calculation step (E64) is less than or equal to a second predetermined threshold, the predetermined amount of fuel of basic setpoint (C11), otherwise. 17. Evaluation method according to one of claims 1 to 16, characterized in that the step (E7) for developing the fuel quality index comprises a step (E71) of integration over time, over the analysis period (TA), the value taken by the magnitude representative of the mechanical torque delivered and / or delivered by the engine. 18. Evaluation method according to one of claims 1 to 17, characterized in that the qualification step (E8) comprises a step (E81) of comparison between the fuel quality index developed in step ( E7) and at least one predetermined threshold. 19. Evaluation method according to claim 18, characterized in that said at least one predetermined threshold depends on the temperature of the coolant coolant of the engine. 20. Evaluation method according to one of claims 1 to 19, characterized in that the physical characteristic associated with the fuel and qualified in the step (E8) qualifying corresponds to the volatility of the fuel. 21. Evaluation method according to one of claims 1 to 20, characterized in that it comprises: - at startup, a step (El)) monitoring changes in the value taken during a monitoring period (TS) ), by a magnitude representative of the difference between the motor setpoint acceleration and the instantaneous engine acceleration, - a step (E2) of elaboration, from the data from the monitoring step (E1)) , a start quality index 25 representative of engine performance during startup, including an energy efficiency of the engine. 22. Evaluation method according to claim 21, characterized in that the monitoring period (TS) is prior to the analysis period (TA) and corresponds to a duration separating a first instant (t1) where the motor has a zero regime and a second instant (t2) where the engine reaches the transient peak regime. 23. Evaluation method according to one of claims 21 and 22, characterized in that the index of quality of start is equal to the ratio between the positive sums (S +) and the absolute value of the negative sums (S-) of the value taken by the magnitude representative of the difference between the setpoint acceleration of the engine and the instantaneous acceleration of the engine. 24. Evaluation method according to one of claims 21 to 23, characterized in that it comprises a step (E3) of weighting of the boot quality index, according to at least one representative information of a condition of the engine during the monitoring period (TS), including a temperature of the intake air and / or the temperature of the coolant coolant of the engine. 25. Evaluation method according to one of claims 21 to 24, characterized in that it comprises a step (E4) for qualifying a chosen starting quality, from the index of quality start-up developed, among predetermined qualitative criteria of startup. 26. Evaluation method according to one of claims 21 to 25, characterized in that it comprises a step (E5) of characterization, from the index of quality of starting, internal mechanical friction of the engine and / or fuel volatility. 27. Evaluation method according to claim 26, characterized in that the volatility of the fuel is obtained by an abacus taking as input the starting quality index and the temperature of the coolant coolant of the engine and outputting the volatility. fuel. 28. Evaluation method according to one of claims 21 to 27, characterized in that it comprises a step (E9) of adjusting the result of the step (E8) of qualification of the physical characteristic associated with the fuel, from the starting quality index resulting from the step (E2) of preparation and / or the starting quality resulting from the step (E4) of qualification of the quality of starting and / or mechanical friction internal engine and / or fuel volatility from the step (E5) of characterization. 29. A method of controlling the heat engine, characterized in that it comprises a phase (P1) during which the evaluation method according to any one of claims 1 to 28 is implemented and a phase (P2) implementation of a motor control method from the data from the evaluation method. 30. The control method as claimed in claim 29, characterized in that the control method comprises a step (E10) for adjusting adjustment parameters associated with the motor, based on the qualitative qualification resulting from the step (E8) of qualification, then a step (El 1) of applying the adjustments adjusted to said adjustment step (E10), said application step (El 1) being implemented during a phase of operation of the engine subsequent to said start and / or during a subsequent engine start. 31. Electronic control unit which implements the evaluation method according to any one of claims 1 to 28 and / or the control method according to any one of claims 29 and 30. Motor vehicle, comprising a heat engine and an electronic control unit according to claim 31. 33. Data storage medium readable by a computer, on which is recorded a computer program comprising computer program code means for implementing the phases and / or steps of a method according to one of claims 1 at 30. 34. Computer program comprising a computer program code means adapted to the realization of the phases and / or steps of a method according to one of claims 1 to 30, when the program is executed by a computer.