EP2191117A1

EP2191117A1 - Method for diagnosing the exchanger bypass flap in an exhaust gas recirculation circuit

Info

Publication number: EP2191117A1
Application number: EP08832422A
Authority: EP
Inventors: Julien Allard; Clément Petit; Ronan Le-Bras
Original assignee: Renault SAS
Current assignee: Renault SAS
Priority date: 2007-09-20
Filing date: 2008-07-25
Publication date: 2010-06-02
Also published as: JP2010539388A; FR2921425B1; JP5241842B2; WO2009037407A1; FR2921425A1

Abstract

The invention relates to a method for diagnosing a failure of the EGR circuit (3) of an engine including an EGR exchanger (31), an EGR valve (33), a bypass duct (35) of the EGR exchanger, and a so-called bypass flap (32) arranged upstream from the EGR exchanger (31) and the bypass duct (35) in order to adjust the proportion of exhaust gases flowing therethrough, wherein the EGR circuit (3) can be activated according to a cooled mode, in which the flap (32) is shut, or according to a bypass mode in which the flap (32) is open, said method comprising carrying out, during a diagnosis phase, two activations (A1, A2) of the flap (32), and measuring an average of the variations of the EGR gas temperature (TsEGR) at the outlet of the EGR exchanger (31) during the diagnosis phase.

Description

METHOD FOR DIAGNOSING THE EXCHANGER DERIVING CIRCUIT IN A GAS RECIRCULATION CIRCUIT

EXHAUST

FIELD OF THE INVENTION

The present invention relates to a method for diagnosing a failure of the EGR circuit of an engine, more specifically the blocking of the bypass flap of the EGR exchanger.

BACKGROUND OF THE INVENTION

The bypass flap is a key element of the exhaust gas recirculation system (designated by the acronym EGR - Exhaust Cas Recirculation according to the English terminology). Its function is to direct the EGR gases into a bypass circuit (or , according to the frequently used Anglo-Saxon terminology, "by-pass") of the exchanger in order to benefit from hot gases for priming the catalyst

The proper functioning of the shutter thus makes it possible to guarantee the depolution of the current diesel engines The blocking of the shutter in bypass mode or in cooled mode has direct consequences on the pollution emitted at the exit of the engine

The abatement thresholds being increasingly severe _"it is essential to meet future standards, diagnose such failures of the flap

The Ise risk blocking component addition is not only related to pollution because _"a failure of the component can affect the reliability of the surrounding components (degradation due to too high a temperature of the EGR valve and its support) and the integrity of the engine control strategies that I use (such as, for example, the slagging of the valve and the exchanger, or the priming of the catalyst) Several methods of fault diagnosis have already been developed, with variable performance

One method, disclosed in JP2006-291921, uses a temperature sensor located at ^the entrance of the inlet manifold and can diagnose the flap becoming jammed by measuring I temperature difference between the cooled mode and the bypass mode, _{however, "this} method, based on a simple difference of the two temperatures, seems very robust vis-à-vis dispersions and variations related to the inertia of the system EβR In addition, this method has the the disadvantage of not allowing to verify the proper closing of the shutter after pressing a blockage in the actuated position pane will be detected at ^the next occurrence of diagnosis Furthermore, this method seems relatively imprecise because the temperature sensor located at the entrance of the intake manifold is influenced by the fresh air admitted

Another method _"described in JP 2003-247459, is implementing a strategy based on the monitoring of the air flow before and after the activation of the bypass flap, the air intake flap and EGR valve is fully open the main advantage of this solution is that it simply uses the meter located on the fresh air intake duct However, according to the technical means used, this strategy can generate a significant false detection rate _" due to the EGR environment (high temperatures _" fouling of the conπectic) and the limited reactivity of the shutter control Indeed, phenomena of pressure waves delay the vacuum control of the bypass flap

Finally, other applications use a contactor to know the open / closed position of the panel However, this strategy can also generate a high rate of false detections, because of the EGR environment

An object of the invention is therefore to define a simple and reliable method for detecting any failure of the bypass flap. Another object of the invention is to diagnose a total loss of the cooling function.

BRIEF DESCRIPTION OF THE INVENTION

A first object of the invention is a method for diagnosing a failure of the EGR circuit of an engine comprising an EGR exchanger, an EGR valve, a bypass duct of the EGR exchanger, and a so-called bypass flap arranged upstream of the EGR exchanger and the bypass duct so as to regulate the proportion of the exhaust gas passing therethrough, the EGR circuit being able to be activated in a so-called cooled mode, where the flap is closed, and a so-called bypass mode, where the shutter is open, the method being characterized in that, during a diagnostic phase, two flap actuations are performed and an average of the changes in the temperature of the EGR gases at the exit of the EGR exchanger is measured during the diagnostic phase. ^• characteristics of the invention

- The first activation aims to open the shutter, and the second activation aims to close the shutter;

the maximum temperature reached during the diagnostic phase is measured,

a first temperature difference is calculated between said maximum temperature and the temperature measured at the time of the first activation and a second temperature difference is calculated between said maximum temperature and the temperature measured at the end of the diagnostic phase;

the average of the first and second temperature differences is calculated,

the average is compared with a predetermined threshold such that: if the average is greater than the threshold, then the component is functional; if the average is below the threshold, then the flap is defective Another object of the invention relates to a diagnostic device for a failure of the EGR circuit of an engine comprising an EGR exchanger. an EGR valve, a bypass pipe of the EGR mixer, and a so-called bypass flap arranged upstream of the EGR exchanger and the bypass duct so as to regulate the proportion of the exhaust gases passing therethrough. , The EGR circuit being able to be activated in a so-called cooled mode, where the shutter is closed, and a so-called bypass mode, where the flap is open, the device comprising a temperature sensor (34) arranged in such a way as to measuring the temperature of the EGR gas exiting the heat exchanger, means for acquiring temperature measurements _"means averaging the measured temperatures, a comparison means with a threshold (S) predetermined a third object of the invention relates to a motor vehicle comprising temperature measuring means and calculation means for implementing the diagnostic method according to the invention

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantages of the invention will appear better on reading the detailed description of the invention which follows, with reference to the appended figures in which "FIG. 1 schematically represents a device for recirculating gases. EGR which ^{is to} apply the invention,

FIG. 2 is a graph illustrating the operating principle of the invention;

FIG. 3 is a logic diagram of the implementation of the diagnosis; Figure 4 is a curve of test results performed with a functional bypass flap;

FIG. 5 is a curve of test results carried out with a blocked bypass flap

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, the engine 1 comprises a fresh air intake circuit 2 comprising an air intake duct 21 and an air flow meter 22. charge in the intake manifold 4 is adjusted by means of an air flap 23

The engine further comprises an EGR gas recirculation circuit 3 comprising a conduit 30 for recirculating exhaust gas EGR, an EGR exchanger 31 and a valve 33 known as an EGR valve for regulating the flow of EGR gas entering the engine. intake distributor 4 A bypass duct 35 is arranged in parallel with the exchanger 31, a bypass flap 32 is arranged upstream thereof so that

when the flap 32 is closed, the EGR gases pass into the exchanger and are cooled therein ("cooled mode"), and

when the flap 32 is open, the EGR gases pass into the bypass duct and retain substantially their high temperature (this mode is called "bypass")

In FIG. 1, the bypass duct 35 is shown schematically as being integrated in the exchanger 31, but this representation is not limiting and it can be found that the bypass ducts are dissociated from the EGR exchanger. A temperature sensor 34 is furthermore disposed between the outlet of the exchanger 31 and the EGR valve 33, so as to measure the temperature

(Note TsEGR) EGR gas exiting the exchanger According to an alternative embodiment, the sensor 34 may also be disposed downstream of the EGR valve 33

The diagnostic strategy is based on the monitoring of the EGR temperature before and after the activation of the exchanger bypass.

a significant variation of TsEGR between the activation (opening) and the closing of the shutter means that the shutter 32 is functional; conversely, a small variation of TsEGR indicates that the shutter 32 is blocked.

The diagnostic principle according to the invention will be described with reference to FIG.

Firstly, it is important to specify the zone and the conditions necessary for the realization of the diagnosis The detection of a failure of the EGR bypass gate is only possible when the operating conditions are stabilized, in order to filtering fluctuations and temperature inertias The operating point of the strategy will be determined according to the temperature differences observed on the stages of the European approval cycle (NEDC), choose those where the temperature difference is more important

The diagnostic strategy is based on the monitoring of the variation of the temperature TsEGR at the outlet of the EGR exchanger 31 _" after actuation of the bypass flap 32. In FIG. 2, the curve C1, in the form of a slot, represents the evolution of the control of the bypass flap 32 during a diagnostic phase The low value corresponds to the cooled mode (that is to say that the flap 32 is closed so that all the EGR gases pass in the exchanger 31) the high value corresponds to the bypass mode (in which the void 32 is opened so that the EGR gases pass into the bypass duct 35)

Curve C2 represents the theoretical evolution of the temperature TsEGR during a diagnostic phase, with the same time scale as that of the curve C1, with a functional flap 32 Curve C3 represents the theoretical evolution of temperature TsEGR during a diagnostic phase, with the same time scale as that of curve C1, with flap 32 failing

When the diagnostic conditions are reached, the bypass flap 32 is actuated so that one goes from the cooled mode to the bypass mode (represented by the arrow A1 on the curve C1). a first acquisition (rated T1) of the TsEGR temperature

The shutter is thus driven in the open position for a first duration t, which must correspond to the average duration to ensure the full opening of the shutter This time is determined on a case by case basis and put under control in terms of aging

The flap is then actuated (arrow A2 on the curve C1) so as to go from the bypass mode to the cooled mode, it is kept closed for a second duration t At the end of this period of time, an acquisition is performed ( T3) of temperature TsEGR The duration of the diagnostic phase is therefore 2t

During the entire diagnostic phase, the maximum temperature (denoted T2) reached at the output of the EGR exchanger is sought. This makes it possible to overcome the thermal inertia of the EGR circuit. It is then possible to calculate a first temperature difference ΔT1 ≈ T2 - T1

This calculation ^is effected about the points 1 (time of opening of the shutter) and point 2 (maximum TsEGR reached during the diagnostic phase) of curve C2 Ia

A second temperature difference ΔT1 = T2-T3 is also calculated. This calculation is performed between point 2 and point 3 (corresponding to the end of the diagnostic phase and the complete closing of the flap) of curve C2.

The diagnostic criterion is the average of these two deviations, which makes it possible to overcome the external disturbances encountered in the current use of a vehicle (road condition, dispersions). This diagnostic criterion is designated by ΔTmoy = (ΔT1 + ΔT2) / 2 The calculation of ΔT1 is performed on the first activation. However, this calculation alone does not make it possible to detect a nuisance blocking of the flap during the course of the diagnosis. It is therefore important to check whether the flap has returned to its position. The second deviation âT2 calculated on the second activation makes it possible to detect it In addition, the calculation of the second difference allows a gain in detection reliability.

With a functional component (curve C2), the activation of the component has a visible impact on the TsEGR temperature, which results in relatively large gaps and .DELTA.T1 .DELTA.T2, typically about 25 ^C C for low efficiency exchangers , up to 100 ⁰ C for exchangers with significant efficiency

For against, with a failing component (curve C3), component of the activation ^has not affect the temperature TsEGR ₁ resulting in very low temperature differentials of the order of 0 to 10 ⁰ C.

Statistical studies are used to determine a threshold. that: s! ΔTmoy = (ΔT1 - * ^• ΔT2) / 2 is greater than S, then the bypass flap is functional; if Δïmoy = (.DELTA.T1 + .DELTA.T2) / 2 is less than S, it is considered that the component fails, the possible failure causes being mechanical seizing, Ie disconnect the hose from ^the valve by-pass, or a order problem

With reference to FIG. 3, the logical process for performing the diagnosis thus comprises the following steps ^*

- When starting the vehicle, the device is initialized (box 101);

- as long as the conditions are not stabilized (box 102), the diagnosis is inactive, when the conditions are stabilized (box 103), the by-pass command is activated and the temperature is memorized TsEGR_1 (box

104),

- then deactivate the bypass command (box 105)

the temperature TsEGR_2 (box 106) is stored,

- is stored Ia TsEGR_3 temperature (Section 107) _"- the temperature differences is calculated ^•

ΔT1 = I TsEGRJ - TsEGR _^ 2

ΔT2 = I TsEGR _^ 2 - TsEGR_3 then we compare the mean of the deviations (âTmoy = (ΔT1 + ΔT2) / 2) with the predetermined threshold S (box 108). ^m if Δmoy <S, a fault is reported (box 109), m if Δmoy> S, the diagnosis is deactivated (box 102)

When the fault is confirmed, information (called by DTC or Diagnostic Trouble Code according to the English terminology) is stored in the computer memory, a service indicator lights, finally, a degraded mode is activated, consisting of closing EGR valve to reduce the temperature at its terminals

Figure 4 shows the results of measuring TsEGR with a functional component

FIG. 5 shows the results of the measurement of TsEGR with the bypass control disconnected

The diagnostic method that has just been presented therefore has the advantage of being based on a very reliable strategy. Indeed, tests carried out on an application with a very low efficiency EGR exchanger have shown the discriminating nature of the âTmoy criterion.

In addition, the proposed method makes it possible to verify that the shutter is properly closed during the same diagnostic phase. Finally, the measurement of the temperature TsEGR requires the use of a temperature sensor, but this measurement does not make it possible to perform the diagnosis of the bypass flap but can be used for other diagnoses - the diagnosis of ^the EGR exchanger, for example, including ia total loss of cooling function failures leading to this loss - water leak example - being nevertheless rarer

Claims

A method for diagnosing a failure of the EGR circuit (3) of an engine comprising an EGR exchanger (31), an EGR valve (33), a bypass duct (35) of the EGR exchanger, and a flap (32). said by-pass, arranged upstream of the EGR exchanger (31) and the bypass duct (35) so as to regulate the proportion of the exhaust gases passing therethrough, the EGR circuit (3) being suitable for being activated in a so-called cooled mode, where the flap (32) is closed, and a so-called bypass mode, where the flap (32) is open, characterized in that, during a diagnostic phase, two activations (A1, A2) of the flap (32) and in that ^one measures the average of the temperature variations (TsEGR) of the EGR gas at the outlet of the EGR exchanger (31) during the diagnostic phase

2 Method according to claim 1 _" characterized in that the first activatïon (A1) aims to open the flap (32), and in that the second activation (A2) aims to close the flap (32)

3 A method according to claim 2 _{"characterized} in that one measures the maximum temperature (T2) reached during the diagnostic phase

4 Process according to claim 3, characterized in that a first temperature difference (ΔT1) is calculated between said maximum temperature (T2) and the temperature (T1) measured at the moment of the first activation (A1) and in that that a second temperature difference (ΔT2) between said maximum temperature (T2) and the temperature (T3) measured at the end of the diagnostic phase is calculated

5. Process according to claim 4, characterized in that the average (ΔTmoy) of the first and second temperature differences is calculated.

6 Process according to claim 5, characterized in that the mean | ΔTmoy) is compared with a predetermined threshold (S) so that If ΔTmoy is greater than S then the pane is functional, if ûTrnoy is less than S, then the pane is defective

7 A device for diagnosing a failure of the EGR circuit (3) of an engine comprising an EGR heat exchanger (31), an EGR valve (33), a bypass duct (35) of ^the EGR heat exchanger, and a flap ( 32) said bypass _"disposed upstream of the EGR exchanger (31) and the bypass duct (35) so as to regulate the proportion of the exhaust gas flowing therein, Ie EGR circuit (3) being able to be activated in a so-called cooled mode, where the flap (32) is closed, and a so-called bypass mode, wherein the flap (32) is open, characterized in that it comprises; a temperature sensor (34) arranged to measure the temperature of the EGR gases leaving the exchanger,

means for acquiring temperature measurements; means for calculating the averages of the measured temperatures;

a means of comparison with a predetermined threshold (S)

8 Motor vehicle, characterized in that it comprises means for measuring temperature and calculation means for implementing the method according to one of claims 1 to 6