FR3048455A1 - METHOD FOR DIAGNOSING AN EGR VALVE - Google Patents

Abstract

The invention relates to a method for diagnosing a recirculation valve (51) which equips a recirculation line (50) for burnt gases of an internal combustion engine (1) and which comprises a mobile part for regulating the flow rate of flue gas circulating in this recirculation line. According to the invention, the diagnostic method comprises steps of: - determining a first value of a torque delivered by the engine, - changing the position of the recirculation valve, - determining a second value of said torque - comparison of the two determined values and deduction of a diagnosis of the recirculation valve.

Description

Technical field to which the invention relates

The present invention generally relates to recirculation of flue gases in an internal combustion engine.

It applies more precisely to an internal combustion engine, comprising: - a fresh air intake line, - an engine block which delimits at least one cylinder in which the intake line opens, - a line of exhaust of the burnt gases which originates in each cylinder, - a recirculation line of flue gas, which originates in the exhaust line, which opens into the intake line, and which comprises a recirculation valve comprising a part mobile adapted to regulate the flow of burnt gases circulating in the recirculation line, - a means for determining the value of the torque delivered by the internal combustion engine, and - a computer adapted to control in position the moving part of said valve of recirculation.

It relates more particularly to a method for diagnosing the recirculation valve of such an internal combustion engine.

Technological background

In an internal combustion engine, the burn gas recirculation line, also known as the EGR line, is designed to take part of the gases burned by the engine in the exhaust line in order to reintroduce them into the intake line with a view to in particular to reduce the polluting emissions of the engine and / or the fuel consumption.

The recirculation valve, also called the EGR valve, then makes it possible to regulate the flow rate of burnt gases injected into the intake line.

There are sometimes failures of this recirculation valve, which can then remain locked in a fixed position. Such blockage leads to a decrease in engine performance and / or an increase in pollutant releases.

It is then clear that it is necessary to ensure the proper functioning of this recirculation valve and quickly diagnose any failure of this valve.

Various methods are currently known for establishing a diagnosis of the recirculation valve.

Document JPH07139437 describes a method using, for the purpose of establishing a diagnosis, a particular parameter which is the "ignition advance".

It is recalled that in a spark ignition engine, the ignition timing corresponds to the delay with which the mixture of fuel and fresh air is ignited in the cylinder, before the piston reaches its top dead center. This ignition advance is then controlled so as to reduce the rate of knocking at best. However, since the knock rate naturally decreases when the recirculation valve opens, it is generally expected to jointly open the recirculation valve and advance ignition to optimize the operation of the engine. It is therefore understood that the ignition advance and the position setpoint of the recirculation valve are two parameters that are, when the valve is working properly, intimately linked.

The diagnostic method proposed in this document JPH07139437 then consists in reading the ignition advance and the position setpoint of the recirculation valve, and in determining whether these values correspond. A poor correspondence of these values then indicates a malfunction of the recirculation valve.

This method has the major disadvantage that it is necessary to wait for the occurrence of rattling, which is recalled that this is a potentially destructive phenomenon for the engine, to diagnose a failure of the valve of recirculation.

Object of the invention

In order to overcome the aforementioned drawback of the state of the art, the present invention proposes a new method of diagnosis, based on the observation of the variation of the torque delivered by the motor during a change of position of the valve. recirculation.

More particularly, there is provided according to the invention a method for diagnosing a recirculation valve comprising steps of: a) determining a first value of a torque delivered by the internal combustion engine, b) changing the position the moving part of the recirculation valve, c) determining a second value of said torque, d) comparing the first and second values determined in steps a) and c), and e) establishing a diagnosis of the valve of recirculation, taking into account the result of the comparison made in step d).

The physical phenomenon used to diagnose a failure of the recirculation valve is then based on the following observation (made by the applicant).

When opening the recirculation valve, the rate of flue gas among the gases admitted to the cylinders increases. The place occupied by these inert gases (neutral in terms of wealth) can then be considered as a reduction of the engine displacement (indeed, there is then less volume to occupy by the fresh gas rich in fuel to burn and oxygen ). This reduction in displacement then causes a drop in the torque produced by the engine.

When closing the recirculation valve, the rate of burnt gases among the gases admitted to the cylinders drops, which is similar to an increase in the engine displacement. This increase in the effective displacement causes a depletion of the fuel mixture (the amount of fuel remaining initially identical for an additional supply of fresh air), which again causes a drop in the torque produced by the engine.

In summary, when the recirculation valve is controlled to open or close, there must be a decrease in the torque produced by the engine. If the torque does not vary, then a malfunction of the recirculation valve can be deduced.

The principle of the proposed diagnosis is then based on the observation of the torque drop when a position change instruction is transmitted to the recirculation valve. The invention is then particularly advantageous for the following reasons.

First of all, it makes it possible to detect a problem of the recirculation valve quickly and efficiently, without waiting for the occurrence of rattling, which makes it possible to remedy this problem all the more quickly and without fear of deterioration of the engine.

This detection is even faster than the diagnostic process can be implemented on most points of operation of the engine (idle, acceleration, steady state, etc.), so that it is not necessary to 'wait a long time before you can implement it.

Furthermore, the invention does not require any particular sensor, in that the only means necessary to implement it (namely the means for acquiring the torque) is already existing on the vehicles currently in circulation. Other advantageous and non-limiting characteristics of the diagnostic method according to the invention are the following: in step d), the difference between the first and second values is compared with a determined threshold; in step e), a malfunction of the recirculation valve is diagnosed if said difference remains below said threshold for a determined duration; - It is intended to acquire data relating to the operating point on which the internal combustion engine operates, and said threshold and said duration are determined according to said data; and - the internal combustion engine comprising at least one cylinder in which a mixture of fresh air and gasoline is regularly burned, in steps a) and c), the torque considered is the average torque produced by the combustion of the fresh air and gasoline intervening in each cylinder. The invention also relates to a vehicle as defined in the introduction, the computer is adapted to implement a diagnostic method as mentioned above.

Advantageously then, the intake line comprises a compressor, the exhaust line comprises a turbine coupled to the compressor, and the recirculation line starts in the exhaust line downstream of the turbine and opens into the intake line. upstream of the compressor.

Preferably, the determination means comprises, on the one hand, a target which is provided with teeth and which is integral with the crankshaft of the engine block, and. on the other hand, a fixed sensor located opposite the target and adapted to deliver to the computer a signal relating to the speed of movement of the teeth of the target.

Detailed description of an example of realization

The following description with reference to the accompanying drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be achieved.

In the accompanying drawings: - Figure 1 is a schematic view of an internal combustion engine according to the invention; FIG. 2 is a logic diagram illustrating the steps of implementing a diagnostic method according to the invention; and FIGS. 3A and 3B respectively illustrate the variations over time of a fire torque and of an opening angle of a control valve of the internal combustion engine of FIG. 1.

In the description, the terms "upstream" and "downstream" will be used in the direction of the flow of gases, from the point of collection of fresh air into the atmosphere to the exit of the flue gases in the atmosphere. atmosphere.

FIG. 1 diagrammatically shows an internal combustion engine 1 of a motor vehicle, which comprises an engine block 10 provided with a crankshaft 12 and pistons (not shown) which are housed in cylinders 11 and which are connected at the crankshaft 12.

This engine comprises here four cylinders 11, but it could include any other number.

It is called "spark ignition". It comprises for this purpose four spark plugs 13 which open respectively into the four cylinders 11 and which create a spark each cycle of operation of the engine.

Upstream of the cylinders 11, the internal combustion engine 1 comprises an intake line 20 which takes fresh air into the atmosphere and which opens into an air distributor 25 arranged to distribute the fresh air to each of the four cylinders 11 of the engine block 10.

This intake line 20 comprises, in the direction of flow of fresh air, an air filter 21 which filters the fresh air taken from the atmosphere, a compressor 22 which compresses the fresh air filtered by the filter 21, and a main air cooler 23 which cools this compressed fresh air.

It also comprises an intake valve 26 located between the air filter 21 and the compressor 22, which regulates the flow of fresh air admitted by the compressor 22, and a gas valve located between the main air cooler 23 and the air distributor 25, which regulates the flow of air admitted into the cylinders 11.

Here, the intake line 20 further comprises a load shedding line 27, which bypasses the compressor 22 and which is equipped with a valve 28 for discharging fresh air pressure into the intake line. 20.

At the outlet of the cylinders 11, the internal combustion engine 1 comprises an exhaust line 30 which extends from an exhaust manifold 31 into which the gases that have been previously burned into the cylinders 11, up to a silencer exhaust 34 to relax the burnt gases before they are discharged into the atmosphere. It also comprises, in the direction of flue gas flow, a turbine 32 and a catalytic converter 33 for the treatment of pollutants contained in the flue gases.

The turbine 32 is rotated by the flow of burnt gases leaving the exhaust manifold 31, and it makes it possible to drive the compressor 22 in rotation, thanks to mechanical coupling means such as a simple transmission shaft.

The exhaust line 30 also comprises a short-circuiting duct 35 of the turbine 32, which is equipped with a control valve 36 of the flue gas flow therethrough.

The internal combustion engine 1 also comprises at least one recirculation line, making it possible to withdraw a portion of the flue gases circulating in the exhaust line 30 in order to introduce it into the intake line 20.

It comprises here a single recirculation line, called "low pressure recirculation line 50" or "line EGR-LP 50" (according to the acronym "Exhaust Gas Recirculation - Low Pressure"). It originates in the exhaust line 30, at the outlet of the catalytic converter 33, and opens into the intake line 20, between the air filter 21 and the compressor 22. This line EGR-LP 50 comprises, d a part, a heat exchanger 52 for cooling the burnt gases borrowing it, and, secondly, a control valve 51 called valve EGR-LP 51. This valve EGR-LP 51 comprises a fixed frame which encloses a moving part , such as a pivoting flap, for regulating the flow rate of flue gases flowing in the line EGR-LP 50. For simplicity, the use of the expression opening or closing of the valve will designate more precisely in the following this presentation the opening or closing of the pivoting flap.

In addition or alternatively, as shown by the portion shown in dashed lines in FIG. 1, the internal combustion engine 1 could comprise a high pressure recirculation line 40, originating in the exhaust line 30, between the collector exhaust 31 and the turbine 32, and opening into the inlet line 20, between the compressor 22 and the air distributor 25. This high pressure recirculation line 40 would then include a heat exchanger 42 for cooling the burnt gases, and a valve 41 to regulate the flow of burnt gases.

The internal combustion engine 1 also comprises a fuel injection line 60 in the cylinders 11. This injection line 60 comprises an injection pump 62 arranged to collect the fuel in a reservoir 61 to bring it under pressure in a distribution rail 63. This injection line 60 further comprises four injectors 64 whose inputs communicate with the distribution rail 63 and whose outlets open respectively into the four cylinders 11.

To control the various components of the internal combustion engine 1 and in particular the valve EGR-LP 51, there is provided a computer 100 comprising a processor (CPU), a random access memory (RAM), a read only memory (ROM), analog converters -numerical (A / D), and different input and output interfaces.

Thanks to its input interfaces, the computer 100 is adapted to receive different sensors input signals relating to the operation of the engine. Thanks to its analog-digital converters, the signals received by the computer are sampled and digitized.

In its random access memory, the computer 100 thus continuously stores: the instantaneous load of the internal combustion engine 1, the instantaneous R speed of the internal combustion engine 1, the water temperature Te of the internal combustion engine 1, and - a scrolling speed ω.

The load corresponds to the ratio of the amount of air admitted by the engine divided by the maximum amount of air that this engine could admit at a given speed. It is usually estimated using a unitless variable.

R regime corresponds to the speed of rotation of the crankshaft 12, expressed in revolutions per minute.

The speed of travel ω is measured by means of acquisition means 70 which, as shown in FIG. 1, comprises, on the one hand, a target 71 which is provided with teeth and which is integral with the crankshaft 12, and, d on the other hand, a fixed sensor 72 which is located opposite the target 71 and which is adapted to deliver to the computer 100 a signal relating to the speed of travel ω of the teeth of the target 71 in front of the fixed sensor 72.

Here, the target 71 is formed by a toothed wheel whose teeth are identical (with the exception of an indexing tooth) and are regularly distributed along its periphery. The fixed sensor 72 is an optical sensor.

The read-only memory (ROM) of the computer 100 stores various data.

It stores in particular a computer application, consisting of computer programs comprising instructions whose execution by the processor allows the implementation by the computer 100 of the method described below. One of these computer programs makes it possible in particular to determine a gas torque C, as a function of the speed of travel ω of the teeth of the target 71 acquired by the fixed sensor 72. The calculation of this gas torque C is already known from the state of the art and not the subject of the present invention, it will not be described here in detail. A method for calculating this gas torque is for example described in patent document FR2757945. It will be noted only that this gas pair C corresponds to the average torque exerted on the crankshaft 12 by the pistons thanks to the combustion of the fresh air and gasoline intervening in each cylinder 11. Consequently, this gas pair C is calculated from so that it is independent of the inertia of the components of the transmission chain of the vehicle, the vibrations of the vehicle, the friction of the wheels on the road ...

The read-only memory of the computer 100 also stores a predetermined map on a test bench, thanks to which the computer is adapted to generate, for each operating condition of the engine, output signals to be transmitted to the various components of the engine, in particular to the EGR-LP valve 51. The object of the present invention is then to diagnose a possible failure of the valve EGR-LP 51 on the basis of the observation of the variation of the gas torque C during a change of position of the EGR-LP valve 51.

FIG. 2 shows the steps of an algorithm implemented by the computer 100 to establish such a diagnosis.

During a first step El, when the driver of the motor vehicle puts the ignition, the computer 100 is initialized then controls the starter and the fuel injectors 64 for them to start the internal combustion engine 1.

When the engine is started (step E2), the fresh air taken from the atmosphere through the intake line 20 is filtered by the air filter 21, compressed by the compressor 22, cooled by the main air cooler 23 , then burned in the cylinders 11 in the presence of fuel. At their outlet from the cylinders 11, the burnt gases are expanded in the turbine 32, treated and filtered in the catalytic converter 33, then relaxed again in the exhaust silencer 34 before being released into the atmosphere.

To operate the engine at a desired operating point Pf, the computer 100 then implements various algorithms, in particular for controlling the valves and the injectors of the internal combustion engine 1.

Here, the operating point Pf is defined by two variables, namely the load and the R-speed of the motor. It is varied when the driver engages a new gear or changes the position of the accelerator pedal.

When the internal combustion engine 1 starts, its water temperature Te is reduced. It then increases progressively until reaching a threshold at which it is then maintained, thanks to heat exchangers.

During the step E2, the operating point Pf and the water temperature Te are then acquired by the computer 100 and stored in its random access memory.

During a step E3, the computer 100 verifies that the operating point Pf and the water temperature Te are such that it is possible to establish a reliable diagnosis of the valve EGR-LP 51.

For this, the computer 100 may for example control that the water temperature Te is greater than a predetermined threshold (the diagnosis is not considered reliable enough when the engine is cold) and that the variation of the speed is below a threshold predetermined (the diagnosis is not considered reliable enough when the engine accelerates very strongly).

As long as these conditions are not met, the process returns to step E2. On the other hand, once they are together, the computer 100 implements a fourth step E4.

During this fourth step E4, the computer 100 receives and records in its RAM the signal emitted by the fixed sensor 72, namely the speed of travel ω of the teeth of the target 71 in front of the fixed sensor 72.

Then, during a step E5, the computer 100 calculates the value Cl of the gas torque C, taking into account the speed of travel ω measured.

During a step E6, of a predetermined duration (for example of the order of a tenth of a second), the computer 100 checks whether a position change instruction is transmitted to the EGR-LP valve 51.

If, at the end of this step E6, no position change instruction has been transmitted to the EGR-LP valve 51, the computer returns to step E5 (or E2).

In the opposite case, the computer implements a step E7, which consists in acquiring a delay D.

This delay D corresponds to the duration at which the value of the gas torque C will be measured again in order to establish a diagnosis of the valve EGR-LP 51.

This delay D is determined according to the operating point Pf of the engine. It is obtained by a reading by the computer 100 of a map stored in its ROM.

This mapping has been previously established during the design of the vehicle, using a battery of tests performed on a vehicle of the same range. It will make each operating point Pf correspond to a determined duration D.

Then, during the steps E8 and E9, the computer 100 suspends the process until the delay D has elapsed.

Once the delay D has elapsed, the computer implements a tenth step E10.

During this step E10, the computer 100 receives and records in its random access memory the signal emitted by the fixed sensor 72, namely the speed of travel ω of the teeth of the target 71 in front of the fixed sensor 72.

Then, during a step El 1, the computer 100 calculates the value C2 of the gas pair C, taking into account the speed of travel ω measured.

Then, the computer 100 implements a step E12, which consists in acquiring a threshold A.

This threshold A corresponds to the amplitude beyond which it is considered that a drop in the gas torque C indicates that the valve EGR-LP 51 is operating correctly.

This threshold A is determined according to the operating point Pf of the engine. It is obtained by a reading by the computer 100 of a map stored in its ROM.

This mapping has been previously established during the design of the vehicle, using a battery of tests performed on a vehicle of the same range. It will make each operating point Pf correspond to a determined threshold A.

Alternatively, it could be provided that this threshold A is not the same depending on whether the valve EGR-LP 51 is controlled to open or close. In practice, the map can then associate each operating point Pf two A thresholds, one of these thresholds being used when the valve is controlled to open and the other being used when the valve is controlled to close.

Then, during a step El 3, the computer 100 checks whether the gas torque drop C is greater than or equal to the threshold A, which can be written: C1-C2> A?

If this is the case, which means that the valve EGR-LP 51 is functional, the computer stores in its RAM an indicator of the proper functioning of this valve (step El4).

In the opposite case, the computer stores in its RAM an indicator of a failure of this valve (step El 5). As an example, he can then take steps to remedy this failure. These measures may consist in transmitting an alert signal to the driver of the vehicle, inviting him to revise his vehicle as soon as possible. They may also consist of controlling the injection of fuel into the cylinders 11 taking into account this malfunction.

In any case, in step E16, the diagnostic process is completed. It can then be implemented either instantly or later (at regular intervals, or after each start of the vehicle, ...).

FIG. 3A shows an example of variation of the fire torque C as a function of the time t while FIG. 3B shows the corresponding variation of the control setpoint Cp of the valve EGR-LP 51 as a function of time t.

In this figure 3B, it is observed that initially, the EGR-LP valve 51 is kept in the closed state because at time to, it is controlled to fully open.

Then, as shown in FIG. 3A, there is a drop in the gas torque C the amplitude of which, measured between times t 1 and t 1 spaced apart by a duration D, is greater than the threshold A, which means that the valve is functioning correctly. .

In FIG. 3B, it is observed later, at time 2, that the valve is controlled to close completely.

Then, as shown in FIG. 3A, a drop in the gas torque C is observed whose amplitude, measured between the times t2 and ts, spaced apart by a duration D, is below the threshold A, which means that the valve is not working. more correctly.

To take account of this malfunction, the computer can then memorize the last position in which the EGR-LP valve 51 was functional, in order to then consider that the valve is locked in this position. The control of the valves and injectors of the engine can then be made taking into account this new parameter, in order to restrict the discharges of pollutants and to avoid as much as possible to harm the performances of the engine.

It is observed here that the thresholds A and the durations D are not the same at times t0 and t2, which is logical since the engine does not operate on the same operating point Pf at these two times.

Furthermore, it can be observed that after the instants t 1 and ts, the gas pair C takes up the value it had before opening or closing the valve EGR-LP 51, which is logical since the computer 100 is controlled for vary the ignition timing and the amount of fuel injected depending on the position of the EGR-LP valve. The gas torque drop C then corresponds to the short time during which the computer has not yet had the time to correct the engine operating parameters to take account of the change of position of the valve EGR-LP 51.

Specifically, after an opening of the valve EGR-LP 51 (comparable to a reduction of the displacement of the engine), the computer 50 can increase the ignition advance, which will optimize the operation of the engine without risk of appearing for as much rattling. In this way, the gas pair C will recover to its initial value.

On the contrary, after a closure of the valve EGR-LP 51 (comparable to an increase in the engine displacement), the computer 50 can increase the amount of fuel injected into the cylinders, which will restore the operation of the engine, and therefore bring back the gas pair C at its initial value.

The present invention is not limited to the embodiment described and shown, but the art can apply any variant within his mind.

Thus, in the embodiment variant in which the motor comprises a high pressure recirculation line 40, it will be possible to implement the diagnostic method in the same manner as explained above, in order to control the proper operation of its valve 41.

Furthermore, in the example illustrated in Figure 3, it was considered that the valve EGR-LP 51 was movable between two stable positions (open and closed). In the case where the valve can take other intermediate positions, it will of course be necessary that the value of the threshold A is a function of the rate of opening or closing of the valve.

Claims (8)

1. A method of diagnosing a recirculation valve (51) which equips a recirculation line (50) of burnt gases of an internal combustion engine (1) and which comprises a mobile part for regulating the flow of flue gases flowing in this recirculation line (50), comprising steps of: a) determining a first value (C1) of a torque (C) delivered by the internal combustion engine (1), b) changing the position of the moving part of the recirculation valve (51), c) determining a second value (C2) of said pair (C), d) comparing the first and second values (C1, C2) determined in steps a) and c) and e) establishing a diagnosis of the recirculation valve (51), taking into account the result of the comparison made in step d). 2. Diagnostic method according to the preceding claim, wherein in step d), the difference between the first and second values (C1, C2) is compared with a threshold (A) determined. 3. Diagnostic method according to the preceding claim, wherein, in step e), a malfunction of the recirculation valve (51) is diagnosed if said deviation is below said threshold (A) for a determined duration (At). 4. Diagnostic method according to the preceding claim, wherein it is intended to acquire data (Pme, R) relating to the operating point (Pf) on which the internal combustion engine (1) operates, and wherein said threshold (A) and said duration (At) are determined according to said data (Pme, R). 5. Diagnostic method according to one of the preceding claims, wherein, the internal combustion engine (1) having at least one cylinder (11) in which a mixture of fresh air and gasoline is regularly burned, the steps a) and c), the torque (C) considered is the average torque produced by the combustion of fresh air and gasoline intervening in each cylinder (11). 6. Internal combustion engine (1), comprising: - a fresh air intake line (20), - an engine block (10) which delimits at least one cylinder (11) into which the line of intake (20), - an exhaust line (30) of the flue gases which originates in each cylinder (11), - a recirculation line (50) of the flue gases, which originates in the exhaust line (30). ), which opens into the inlet line (20), and which comprises a recirculation valve (51) comprising a movable part adapted to regulate the flow of burnt gases circulating in the recirculation line (50), - a means of determining (70) the value (C1, C2) of a torque (C) delivered by the internal combustion engine (1), and - a computer (100) adapted to drive the moving part of said recirculation valve in position (51), characterized in that the computer (100) is adapted to implement a diagnostic method according to one of the preceding claims. 7. Internal combustion engine (1) according to the preceding claim, wherein the intake line (20) comprises a compressor (22), the exhaust line (30) comprises a turbine (32) coupled to the compressor (22). ), and the recirculation line (50) originates in the exhaust line (30) downstream of the turbine (32) and opens into the intake line (20) upstream of the compressor (22). 8. Internal combustion engine (1) according to one of the two preceding claims, wherein the engine block (10) comprises a crankshaft (12), and wherein the determining means (70) comprises, on the one hand , a target (71) which is provided with teeth and which is integral with the crankshaft (12), and, secondly, a fixed sensor (72) located opposite the target (71) and adapted to deliver to the computer ( 100) a signal relating to the speed of movement of the teeth of the target (71).