FR2993935A1 - Method for diagnosing fuel injector of cylinder of thermal engine in car, involves determining state of malfunction of fuel injector representative of poor fuel injection quantity according to generated torque - Google Patents

Abstract

The method involves injecting fuel into a cylinder of a thermal engine by a fuel injector (E1), and combusting the fuel injected into the cylinder (E2). Torque generated according to the combustion of the fuel in the cylinder is determined (E3), and state of malfunction of the fuel injector representative of poor fuel injection quantity is determined (E4) according to the generated torque, where the generated torque is determined by the measurement of pressure in the cylinder, or by the measurement by a torque meter. Independent claims are also included for the following: (1) a computer-readable data recording medium storing a program for diagnosing a fuel injector of a cylinder of a thermal engine (2) a computer program for diagnosing a fuel injector of a cylinder of a thermal engine.

Description

FIELD OF THE INVENTION The invention relates to the field of the motor vehicle. The invention more particularly relates to a method of diagnosing a fuel injector in a heat engine cylinder. STATE OF THE ART In order to comply with future pollution standards, it is necessary to develop a strategy capable of detecting certain failures on combustion of an internal combustion engine and spark ignition engines. Patent FR2681425 discloses the use of a device for measuring a motor torque for detecting misfires. In the case of a misfire, the fuel injected into a cylinder does not explode and is evacuated in the anti-pollution systems. The risk of degradation of the anti-pollution systems is then not negligible because the combustion of the fuel does not take place.

However, there is nothing to identify where the lack of richness present in one of the cylinders, the maintenance operator does not know which room to change.

OBJECT OF THE INVENTION The object of the present invention is to provide a diagnostic solution for poor combustion, in particular due to a failure of the injector. It is aimed at this aim in that the method of diagnosis of a fuel injector of a heat engine cylinder comprises: a step of injecting fuel into the cylinder by the injector; a step of burning the fuel; injected, - a step of determining a torque generated, as a function of the combustion step, by the cylinder, - a diagnostic step configured so as to determine, as a function of the generated torque, a malfunctioning state of the injector representative of a bad amount of injected fuel. According to one implementation, the generated torque is determined from a measurement of pressure in the cylinder, or is determined from a measurement by a torque-meter.

According to one implementation, the diagnostic step may include a step of comparing the generated torque with a first comparison datum, in particular a datum representative of the pair of other cylinders of the motor or a first torque threshold, injector being diagnosed, according to the result of the comparison step, in a poor type of malfunction corresponding to a too small amount injected. Advantageously, the first comparison data being the first torque threshold, the injector is diagnosed in the lean malfunction state if the generated torque is lower than said first threshold. According to another embodiment, the injection step being performed by reducing the normal injection time associated with the cylinder, during the diagnostic step the injector is diagnosed in a state of rich type dysfunction if combustion step has no combustion misfire and / or if during a comparison of the generated torque with a second comparison data, in particular a data representative of the torque of other engine cylinders or a second torque threshold , the result of the comparison is representative of the state of dysfunction of rich type. Advantageously, the second data being a second torque threshold, the result of the comparison is representative of the rich type malfunction state if the generated torque is greater than said second threshold.

Preferably, the injector of the cylinder is diagnosed by taking into account the comparison of the generated torque with the second data over several cycles of injection, combustion, and torque determination generated by implementing for each cycle a step of injection whose normal injection time is decreased so as to confirm the state of rich type dysfunction.

According to a variant, the method comprises a first cycle comprising the injection, combustion, determination of the generated torque, and diagnosis steps according to the corresponding implementation described above, and it comprises, only if during the first cycle the injector is not diagnosed in the state of poor type malfunction, a second cycle comprising new stages of injection, combustion, determination of the generated torque, and a diagnostic step according to the other implementation described above. The invention also relates to a motor vehicle comprising the software and / or hardware means for implementing the method as described. The invention also relates to a data storage medium readable by a computer, on which is recorded a computer program comprising computer program code means for implementing the steps of a method as described.

The invention also relates to a computer program comprising a computer program code means adapted to performing the steps of a method as described, when the program is executed by a computer.25 Brief description of the drawings Other advantages and features will emerge more clearly from the following description of particular embodiments of the invention given as non-limiting examples and shown in the accompanying drawings, in which: - Figure 1 is a diagram illustrating a diagnostic method according to one embodiment of the invention, - Figure 2 illustrates the evolution of the engine speed as a function of time on a four-cylinder engine, - Figure 3 illustrates a curve representative of the evolution of the torque generated by a cylinder. depending on the fuel injection richness, FIG. 4 illustrates a flow diagram of a particular implementation of a diagn method. OSTIC. DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION The method described below differs from the prior art in particular in that a torque generated by combustion in a cylinder is used to detect a malfunction of the injector associated with the cylinder. In FIG. 1, the method of diagnosing a fuel injector of a thermal engine cylinder, in particular of a motor vehicle, comprises a fuel injection step E1 in the cylinder by the injector. Then, a combustion step E2 of the injected fuel is carried out. The combustion step E2 is conventionally carried out by compression of the injected fuel, an ignition and an explosion causing a relaxation at the cylinder resulting, for example, a crankshaft. On the other hand, the method comprises a step E3 determination of a generated torque, a function of the combustion step E2, the cylinder. The generated torque can be determined from a pressure measurement in the cylinder, or can be determined from a measurement by a torque-meter. Once the data has been measured, a software strategy can be implemented to determine the torque associated with said cylinder. Even when the engine has several cylinders, the software strategy can determine the torque associated with each cylinder. To determine the torque by pressure measurement, the cylinder will, for example, be equipped with a pressure sensor arranged in a suitable manner in the combustion chamber of the cylinder.

A pair-meter allows the application of a principle stating that the torque of a cylinder is proportional to the magnitude of the variations of the instantaneous speed of the crankshaft, and can be determined as a function of a measurement of movement of teeth. a crown integral with the crankshaft. Thus, the pair-meter used in the present method may be of the type described in patent FR2681425.

Here the torque meter can detect a simple drift of the amount of fuel injected that does not lead to misfire. The method further comprises a diagnostic step E4 configured so as to determine, as a function of the torque generated, a malfunctioning state of the injector representative of a bad quantity of fuel injected.

In fact, a malfunction state can be of rich type or of poor type. In the case of a poor type of malfunction, this means that the amount of fuel injected was too low (for example a too low flow rate on the injector concerned) compared to the quantity required by the cylinder. A poor type of malfunction can generate significant combustion misfires, or a drop in engine torque at a given moment. In the case of a malfunctioning type rich state, it means that the amount of fuel injected was too much compared to the amount required by the cylinder (eg too high flow). A malfunction of rich type can generate a misfire, or a normal combustion but causing a rejection of fuel at the output of the engine. The detection of these two states has been made interesting following tests carried out to meet anti-pollution standards.

Indeed, the tests have shown that a "poor injector" malfunction leads to an exceedance of antipollution standards for depletion values causing including misfires on the cylinder in default. In the acyclism of the flywheel, this results in a deceleration of the crankshaft during the combustion / expansion phase of the cylinder in default, instead of acceleration due to the pressure work on a non-faulty cylinder. The analysis using a torque meter invariably leads to a strong underestimation of the torque relative to the torque of the other cylinders. Indeed, the torque meter relies on a harmonic analysis of the speed signal on each high engine point (PMH) of a cylinder. On a high motor point with combustion, we obtain a non-zero harmonic value (sinusoidal signal), while the harmonic obtained on a high engine point without combustion will be close to 0 or negative. The average torque per cylinder estimated by the torque-meter strategy will therefore have a value close to 0 for all the estimated pairs of an associated cylinder. This value close to 0 is associated with a faulty injector. A simply worse combustion will be more difficult to detect because it can still generate enough torque.

Figure 2 illustrates the principle of a misfire. This figure gives the evolution of the engine speed over time for a four-cylinder engine respectively labeled PMH Cyl 1-2, PMH Cyl 1-1, PMH Cyl 1, PMH Cyl 1 + 1. At PMH Cyl 1 + 2 rolls were made, ie PMH Cyl 1 + 2 is the same cylinder as PMH Cyl 1-2. On the cylinder PMH Cyl 1 a misfire is observed inducing that no acceleration is given to the crankshaft by the cylinder PMH Cyl 1, the re-acceleration being given by the cylinder PMH Cyl 1 + 1, before re-stabilizing the regime cylinder engine PMH Cyl 1 + 2. This example deals with the case where there is a misfire, that is to say no acceleration given. In the case of a simple drift towards the poverty of the injection, the acceleration will be present but weak, which will induce a loss of average engine speed which will then need to be restored.

On the other hand, a "rich injector" malfunction results in exceeding the anti-pollution standards for enrichment values greater than the injector dispersions. It follows from these findings an importance of detecting a malfunction of an injector. Hereinafter, strategies will be described for detecting a poor type of malfunction state, or a type rich malfunction state. In order to understand the implementation of these strategies, Figure 3 illustrates a curve of the evolution of torque as a function of wealth. Between 0 and 0.7, the mixture in the cylinder will result in a misfire situation, between 0.7 and 1.0 the mixture in the cylinder is a lean mixture. Between 1.0 and 1.1 the mixture is ideal to avoid the problems mentioned above. Beyond 1.1, the mixture is too rich. On reading this curve, it can be seen that in order to detect a drift towards a poor type of malfunction state, the torque generated by the combustion in the cylinder can be compared to a threshold because below 1.0 the slope of the curve is large enough to avoid the detection defects, against above 1.1 the slope of the curve is relatively low, which can lead to problems of detection of the type of malfunction rich type. This is due to the fact that in case of simple drift of the injector on the "rich" side (here we exclude the case of drowning not involving combustion) the cylinder chamber containing more fuel, the pressure due to explosion in the cylinder will remain substantially the same, and therefore the torque will be substantially identical to a torque generated by a perfectly adjusted injector. According to a first implementation, the diagnostic step E4 may comprise a step of comparing the generated torque with a first comparison datum. This first comparison datum may be, in particular, a datum representative of the pair of other cylinders of the engine or a first torque threshold. The injector is then diagnosed, according to the result of the comparison step, in a poor type of malfunction state, for example this poor type corresponds to an injected quantity that is too low, that is to say insufficient. For example, if the first comparison data is the first torque threshold, the injector is diagnosed in the lean malfunction state if the generated torque is lower than said first threshold.

According to a second implementation, the injection step E1 is performed by reducing the normal injection time associated with the cylinder. By "normal time" is meant the time used by the engine computer to control an injector during operation of the vehicle, in the field this period is also commonly called nominal time. Thus, during the diagnostic step E4, the injector is diagnosed in a state of dysfunction of rich type (for example this rich type corresponds to a too much injected quantity) if the combustion step does not present a failure. combustion and / or if during a comparison of the generated torque with a second comparison data, in particular a data representative of the pair of other cylinders of the engine or a second torque threshold, the result of the comparison is representative of the malfunction state of rich type.

For example, the second data being a second torque threshold, the result of the comparison is representative of the rich type malfunction state if the generated torque is greater than said second threshold. The first threshold may be equal to the second threshold. The first data can be identical to the second data. Preferably, the injector of the cylinder is diagnosed by taking into account the comparison of the generated torque with the second data over several cycles of injection, combustion, and torque determination generated by implementing for each cycle a step of injection whose normal injection time is decreased so as to confirm a state of rich type dysfunction. This limits the risk of misdiagnosis. Indeed, the increase in the number of diagnoses makes it possible to reduce the number of false detections. In fact, based on the interpretation of Figure 3, the curve of torque is deliberately shifted as a function of wealth to the left by reducing the normal injection time. Thus, a normally functioning injector will in this case have misfires or a poor type of malfunction, whereas if an injector is in a rich type of malfunction, it will behave like an injector operating normally even with the decrease. voluntary injection time. These first and second implementations can be combined. In other words, the method may comprise a first cycle comprising the injection steps E1, combustion E2, determination of the generated torque E3, and diagnostic E4 according to the first implementation and optionally its variants or embodiments, and the method comprises, only if during the first cycle the injector is not diagnosed in the state of poor type malfunction, a second cycle comprising new injection stages E1, combustion E2, determination of the generated torque E3, and a diagnostic step E4 according to the second implementation and optionally its variants or embodiments. According to a particular embodiment illustrated in FIG. 4, the diagnostic method comprises an initialization step Ei comprising a monitoring step Ei-1 of the diagnostic conditions and a verification step of the diagnostic conditions Ei-2 as a function of the monitoring data from step Ei-1. This method assumes that the heat engine comprises a plurality of cylinders each comprising at least one injector. If the conditions are not met (output not Ei-2), we loop on step Ei-1. If the conditions are satisfied (yes output of Ei-2), it is sought to determine (E3) for each cylinder the torque generated by said cylinder during a combustion associated with an injection (the steps E1 and E2 are not represented in FIG. this logigram, nevertheless it is implicit that to determine the torque of each cylinder, these steps were carried out at the level of each cylinder). The step E3 for determining the torque therefore comprises, for each cylinder, a step E3-1 for measuring pressure, or a measurement of a signal, for example of scrolling of teeth associated with the rotation of a crankshaft (use of a torque meter). This step E3-1 is then associated with a step E3-2 software torque calculation. In fact, this step E3-2 makes it possible to exploit the results of step E3-1 so as to determine a generated torque for each cylinder.

Then, the diagnostic step E4 can be performed. Firstly, all the injectors will be tested E4-1 so as to classify the cylinders in a first set E4-2 or in a second set E4-3. The first set E4-2 comprises the injectors associated with cylinders whose torque is insufficient, that is to say that the injector is considered in the state of lean malfunction. The second set E4-3 then comprises the remainder, that is to say the injectors associated with cylinders whose operation is normal, and the injectors associated with the cylinders whose operation is in a state of dysfunction of rich type. This classification can be achieved by implementing the first implementation described above. Once the first set and the second set determined, each cylinder of the second set will undergo a check so as to know if its injector is normal or in a state of malfunction rich type. In other words, the method comprises from the second set E4-3, a verification step E4-4 of an unverified cylinder of the second set. This verification step can implement the second implementation described above. This verification step makes it possible in other words to determine whether the torque of the checked cylinder is low when the fuel injection time in the cylinder by the associated injector is decreased. If this torque is low (yes output) then the cylinder injector has no fault E4-5. If the torque is sufficient when in fact the injection time has voluntarily been decreased, the injector is diagnosed in the state of E4-6 rich type malfunction. At the output of step E4-6 and of step E4-5, the method proceeds to a step E4-7 during which it is determined whether all the cylinders of the second set have been checked, if yes the process is terminated E4-8, if not then the process returns to step E4-4.

In general, when the engine comprises several cylinders, to detect a possible state of rich-type malfunction of a set of cylinders that are not in a poor type of malfunction, each cylinder of said set is checked one by one. after another. That is, for a given cylinder in checking, the fuel injection time of its associated injector is decreased while the injection time remains normal (that is to say higher) for the other engine cylinders. This makes it possible to isolate the cylinder to be checked and for example to facilitate the diagnosis of its injector during a comparison of its generated torque with the torque of the other cylinders. The implementation of a method as described above in its various implementations makes it possible to detect the rich or poor drift of an injector, and to precisely target the faulty injector so as to orient the repairer to the correct one. cylinder. This avoids the unjustified disassembly of an engine during maintenance.

In order to ensure the quality of detection of the diagnostic process, a validation plan must be built taking into account the dispersions tolerated by each injector. In other words, the comparison data will be adapted according to the type of injector. For example, taking the ideal torque that should provide a cylinder for a given injection, the tolerance is of the order of 10Nm to 15Nm is about a fuel quantity tolerance injected 3mg / stroke.

The strategy implemented to detect an injector in a state of dysfunction of rich type implementing a decrease in the injection time being intrusive, it is preferable that the latter takes place when the engine is in steady state. By "stabilized" is meant minimum variations in fuel flow injected into each cylinder. The advantages of the method as described are multiple, in particular we will have: - A use of proven algorithms; - No additional cost related to new engine control components (no specific flywheel target, no new sensor or ASIC ...); - Simplicity of operation which ensures a good robustness of the detection; - The novelties in term of algorithms are limited: little extra costs in memory and / or in calculation time; - Meets Onboard Diagnostics OBD (On Board Diagnostics) objectives.

In general, the process can be applied to internal combustion (thermal) and spark ignition, direct or indirect fuel injection and n-cylinder (s) rotary engines. A motor vehicle may comprise the software and / or hardware means for implementing the method as described above. A computer readable data storage medium on which a computer program is recorded may include computer program code means for implementing the steps of the method as described.

A computer program may include a computer program code means adapted to perform the steps of a method as described, when the program is executed by a computer.

Claims (11)

REVENDICATIONS1. A method of diagnosing a fuel injector of a heat engine cylinder, characterized in that it comprises: - a fuel injection step (El)) in the cylinder by the injector, - a combustion step (E2) injected fuel, - a step of determining (E3) a generated torque, a function of the combustion step (E2), by the cylinder, - a diagnostic step (E4) configured to determine, depending on the torque generated, a state of malfunction of the injector representative of a wrong amount of injected fuel. 2. Method according to claim 1, characterized in that the generated torque is determined from a pressure measurement in the cylinder, or is determined from a measurement by a torque meter. 3. Method according to one of claims 1 or 2, characterized in that the diagnostic step (E4) comprises a step of comparing the generated torque with a first comparison data, including a data representative of the torque of other cylinders of the motor or a first torque threshold, the injector being diagnosed, according to the result of the comparison step, in a poor type of malfunction corresponding to a too small injected amount. 4. Method according to claim 3, characterized in that the first comparison data being the first torque threshold, the injector is diagnosed in the lean malfunction state if the generated torque is less than said first threshold. 5. Method according to one of claims 1 or 2, characterized in that the injection step (El)) being performed by reducing the normal injection time associated with the cylinder, during the diagnostic step (E4 ) the injector is diagnosed in a rich-type malfunction state if the combustion step does not exhibit a combustion misfire and / or if during a comparison of the generated torque with a second comparison data, in particular a representative datum of the pair of other cylinders of the motor or a second torque threshold, the result of the comparison is representative of the state of malfunction of rich type. 6. Method according to the preceding claim, characterized in that the second data being a second torque threshold, the result of the comparison is representative of the rich type of malfunction state if the generated torque is greater than said second threshold. 7. Method according to one of claims 5 or 6, characterized in that the injector of the cylinder is diagnosed taking into account the comparison of the generated torque with the second data on several injection cycles, combustion, and determination torque generated by implementing for each cycle an injection step whose normal injection time is decreased so as to confirm the state of rich type malfunction. 8. Method according to claims 3 and 5, characterized in that it comprises a first cycle comprising the injection (El), combustion (E2), determination of the generated torque (E3), and diagnosis (E4) ) according to claim 3, and in that it comprises, only if during the first cycle the injector is not diagnosed in the state of lean malfunction, a second cycle comprising new injection steps ( El), combustion (E2), determination of the generated torque (E3), and a diagnostic step (E4) according to claim 5. 9. Motor vehicle comprising the software means and / or hardware for implementing the method according to the preceding claims. A computer readable data storage medium, on which is recorded a computer program comprising computer program code means for implementing the steps of a method according to one of claims 1 to 8. A computer program comprising computer program code means adapted to perform the steps of a method according to one of claims 1 to 8, when the program is executed by a computer.