FR2972221A1 - Method for diagnosing failure of member i.e. oxidation catalyst, in exhaust gas line of internal combustion engine i.e. diesel engine, of car, involves measuring nitrogen oxide rate at two temperature levels downstream of reduction member - Google Patents

Abstract

The method involves measuring rate of nitrogen oxide at two temperature levels along direction of flow of exhaust gases (90) downstream of a selective catalytic reduction (SCR) member (60). Failure of an oxidation catalyst (40) is determined when the measured rate of nitrogen oxide at one of the temperature levels corresponds a level inadequate for functioning of the SCR member and the measured rate of nitrogen oxides at the other temperature level does not corresponds to a level inadequate for functioning of the SCR member. An independent claim is also included for a car.

Description

METHOD FOR DIAGNOSING AN EXHAUST LINE BY MEASURING THE NITROGEN OXIDE RATE IN DOWNSTREAM OF A SELECTIVE CATALYTIC REDUCING MEMBER AND CORRESPONDING VEHICLE

The present invention relates to a method for diagnosing failure of an organ in a gas exhaust line from an internal combustion engine. The invention also relates to a motor vehicle comprising an exhaust line and a computer implementing the above method. In the field of the automotive industry, the reduction of fuel consumption and the decrease in the emission of pollutants emitted in the exhaust are major problems. Thus, carbon monoxides (abbreviated as CO) and hydrocarbons (abbreviated as HC) are pollutants whose aim is to reduce the emission into the atmosphere. For the reduction of these pollutants, it is known to use an oxidation catalyst. Such an oxidation catalyst is also known by the abbreviated term CatOx or the abbreviated English Oxydation Catalyst DOC. In the following document, the abbreviation "DOC" and the term "oxidation catalyst" are used interchangeably. [0004] In addition, nitrogen monoxide (NO), nitrogen dioxide (NO2) and nitrous oxide (N2O) are other polluting gases generally known as NO. It is remarkable that the DOC does not contribute to the overall decrease in the emission of NO because DOC, by virtue of its oxidizing characteristics, catalyzes the reaction of formation of nitrogen oxides from nitric oxide. Thus the DOC contributes to the increase of the ratio of nitrogen oxides by nitrogen oxides, noted ratio NO2 / NO in the rest of the document. It is therefore all the more useful to provide a specific organ for the decontamination of nitrogen dioxide and all the nitrogen oxides in particular. The means typically used for the removal of these gases are selective catalytic reduction (Selective Catalytic Reduction SCR abbreviated organs) associated with an injection of urea or NH3. In the rest of this document, the abbreviation "SCR" and the term "selective catalytic reduction" are used interchangeably. Thus the DOC and the SCR member are conventionally integrated in a gas exhaust line from an internal combustion engine. FIG. 1 shows an example of an exhaust line 20 associated with the internal combustion engine 80. This exhaust line 20 can comprise the DOC 40 and the SCR member 60 in this order according to the direction of the exhaust of the gases. 90. To ensure the efficiency over time of the pollution control members present in the exhaust line 20, various methods for diagnosing the failure of these pollution control members have been proposed. A first type of process is based on the modeling of the operating parameters of the exhaust line to diagnose a failure of the exhaust line. Thus the document W02010 / 113269 A proposes an estimated calculation of the NO2 level in the exhaust line to determine a failure of the line. This first type of process does not determine the actual values of the operating parameters of the exhaust line, the reliability of such processes is perfectible. A second type of method is based on the measurement of the actual values of the operating parameters of the exhaust line. The documents WO2008 / 093616 A, WO2009 / 101728 A and DE 10328856 A describe, for example, methods for diagnosing DOC failure by measuring the NOX level at the DOC exit, and possibly upstream of the DOC. Thus these diagnostic methods of the second type propose the use of a specific sensor for detecting the failure of the DOC. The use of specific sensor then leads to obtaining a more complex exhaust line and therefore more expensive. [0010] There is therefore a need for a reliable method of failure diagnosis of a depollution device in an exhaust line, the remaining exhaust line of simple design. For this, the invention proposes a method for diagnosing the failure of an organ in a gas exhaust line from an internal combustion engine, the exhaust line comprising, according to the exhaust direction of the gas, an oxidation catalyst and a selective catalytic reduction member, the process comprising: - measuring at a first temperature and at a second temperature the nitrogen oxide content downstream of the selective catalytic reduction member according to the exhaust direction of the gases, the second temperature being higher than the first temperature; and determining a failure of the oxidation catalyst when: at the first temperature, the measured nitrogen oxide level corresponds to an operating failure of the selective catalytic reduction member; and that at the second temperature, the measured nitrogen oxide level does not correspond to an operating failure of the selective catalytic reduction member. According to a variant, at least one of the first and second temperatures is a temperature measured at the level of the selective catalytic reduction member. According to one variant, at least one of the first and second temperatures is an estimated temperature of the selective catalytic reduction member, the estimate being made by a temperature model of the exhaust line. According to one variant, the temperature model is based on at least one of the parameters of the group of parameters consisting of: the engine speed; - the engine torque; - the fuel flow of the engine; - the fuel phasing of the engine; The air flow of the engine; - the rate of recirculation in the gas engine to escape in the exhaust line; - the winnowing at the intake of the engine; the speed of a vehicle comprising the engine and the exhaust line; and the position of a turbocharger of the engine intake recovering the kinetic energy of the gases to escape into the exhaust line. According to a variant, the method comprises the determination of a failure of the selective catalytic reduction member when, at the first temperature and at the second temperature, the nitrogen oxide levels measured correspond to an operating failure. of the selective catalytic reduction member. According to one variant, to at least one of the first and second temperatures, the measured nitrogen oxide level corresponds to an insufficiency of operation of the selective catalytic reduction member when the oxidation rate of the oxides of measured nitrogen exceeds a predetermined nitrogen oxide threshold of failure. According to one variant, to at least one of the first and second temperatures, the process comprises the calculation of the conversion rate of the nitrogen oxides by the selective catalytic reduction member from the level of oxides of carbon atoms. measured nitrogen, the nitrogen oxide content measured at at least one of the first and second temperatures corresponding to an operating failure of the selective catalytic reduction member when the conversion rate of nitrogen oxides calculated passes below a predetermined conversion threshold of failure. According to a variant: the first temperature is a normal operating temperature of the exhaust line and is between 150 ° C and 300 ° C; and the second temperature is a high operating temperature of the exhaust line and is greater than or equal to 300 ° C. According to a variant, the internal combustion engine from which the gases to escape in the exhaust line is a diesel engine. The invention also proposes a motor vehicle comprising an internal combustion engine, a gas exhaust line of the internal combustion engine and a diagnostic computer of the exhaust line, the exhaust line comprising, according to the gas escape direction, an oxidation catalyst, a selective catalytic reduction member, a nitrogen oxide rate sensor; and the computer implementing the preceding diagnostic method. Other features and advantages of the invention will appear on reading the following detailed description of the embodiments of the invention, given by way of example only and with reference to the drawings which show: FIG. 1 a schematic representation of an exhaust line associated with an internal combustion engine; FIG. 2, a graph comparing the evolution of the ratio of nitrogen oxides by nitrogen oxides for new and old oxidation catalysts; FIG. 3, a three-dimensional graph of the efficiency of the treatment of nitrogen oxides by the exhaust line of FIG. 1 as a function of the temperature and the ratio of nitrogen oxides by nitrogen oxides; FIG. 4, a histogram of the efficiency of the treatment of nitrogen oxides by the exhaust line of FIG. 1 as a function of the ratio of nitrogen oxides by nitrogen oxides at a first and a second temperature; - Figure 5, a graph comparing the temperature evolution for new and old oxidation catalysts. It is proposed a method of diagnosis of failure of an organ in an exhaust line. The diagnosis is intended to be implemented in an exhaust line for gases from an internal combustion engine. The internal combustion engine is preferably a diesel engine. Reference is made to FIG. 1 previously described to illustrate the presence of a DOC 40 and a selective catalytic reduction member 60 in the exhaust line 20. According to this FIG. 1, in the exhaust line For which the proposed process is carried out, the selective catalytic reduction member 60 is downstream of the DOC 20 in the direction of gas exhaust 90. In the rest of this document, the uses of the terms "downstream" and "upstream" describe, in the exhaust line 20, the positioning of a device relative to another device in the direction of the exhaust gases 90 in the exhaust line 20. The method comprises measurements of the nitrogen oxide content downstream of the SCR member 60. These measurements of the NOX level are carried out at a first temperature Ti and at a second temperature T2. T2 is higher than Ti. Indeed, Ti may correspond to a low or average operating temperature of the exhaust line 20 while T2 may correspond to a high operating temperature of the exhaust line 20. Ti then preferably corresponds to a temperature between 150 ° C and 300 ° C whereas T2 preferably corresponds to a temperature greater than or equal to 300 ° C. The method also comprises the determination of a failure of the DOC 40. Indeed, among the known failures of the DOC 40, the aging of the DOC 40 has in particular a consequence of a reduction in oxidation efficiency. HC and CO and a decrease in the NO2 / NOX ratio downstream of the DOC 40. Figure 2 shows a graph comparing the evolution of the NO2 / NOX ratio for a DOC 40 in the new state (curve 70) and for a DOC 40 in the old state (curve 72). The evolution of the NO2 / NOX ratio for each DOC 40 is linked to the same standard operating profile undergone by the internal combustion engine 80. FIG. 2 thus shows the evolution of the speed of the engine 80, when the engine 80 is subjected to the standard operating profile (curve 78). However, the reduction of the NO2 / NOX ratio downstream of the DOC 40 may result in an increase in NOx emissions downstream of the SCR 60 member. This increase in NOx emissions downstream of the SCR 60 member is produced at low or medium temperature of the organ SCR 60, due to a poorer efficiency of the SCR at these temperatures. This reduction in the efficiency of the SCR at low or medium temperature is visible on the web 76 of FIG. 3 which represents a graph of the efficiency of the treatment of NOX by the exhaust line 20 as a function of the NO 2 / NOX ratio. . Temperatures Ti and T2 preferably correspond to the temperature of the SCR 60 member, Ti then corresponds to a low or average temperature of the SCR 60 member. [0028] Thus, by reducing the effectiveness of the SCR by decreasing the NO2 / NOX ratio at low and medium temperature, it is possible to determine a failure in the exhaust line by measuring the NOX level downstream of the SCR member 60 at the temperature Ti. However, it may be useful to discriminate, among the DOC 40 and the SCR member 60, which is the failing organ. In the case where the DOC 40 is defective while the exhaust line 20 is subjected to a high temperature, the decrease of the ratio NO2 / NOX, downstream of DOC 40 due to its failure, does not cause a significant decrease in the effectiveness of the NOX treatment by the SCR 60 organ. Indeed, according to FIG. 3, the decrease in the efficiency of the NOX treatment by the SCR 60 organ is much lower for a high temperature. of the SCR 60 member only for the low and medium temperatures of the SCR member 60. FIG. 4 shows a histogram of NOX treatment efficiency versus NO2 / NOX ratio at Ti and T2. This histogram also shows that the decrease in the NOX treatment efficiency as a function of the NO2 / NOX ratio is significant only at the temperature Ti and not at the temperature T2. Thus at usual temperatures (Ti), the NOx treatment efficiency by the SCR 60 member is dependent on the NO2 / NOX ratio, while it is no longer at high temperatures (T2). Conversely, in the case where the SCR member fails, the efficiency of the NOX treatment decreases downstream of the SCR member 60 regardless of the temperature of the SCR member 60. In other words, a failure of the DOC can be determined when: at the first temperature Ti, the measured NOX level corresponds to an operating failure of the SCR member 60; and that at the second temperature T2, the measured NOX level does not correspond to a failure of operation of the SCR member 60. When the measured NOX level does not correspond to an insufficient operation of the SCR member 60, this means that the measured NOX level corresponds to a satisfactory operation of the SCR member 60, that is to say to a normal operation of the SCR member 60. [0034] can determine that the NOX levels measured downstream of the SCR member 60 correspond or do not correspond to an operating failure of the SCR member 60, according to at least one of the following two determination modes. At a given temperature, Ti or T2, the operating failure of the SCR member 60 may, for example, correspond to a measured nitrogen oxide level exceeding a threshold of predetermined nitrogen oxides of failure. . The predetermined nitrogen oxide threshold of failure preferably depends on the temperature, Ti or T2, of the measurement of the NOX level with which the threshold is compared. At a given temperature, Ti or T2, the operating failure of the SCR member 60 can be further identified by means of a calculation of the NOx conversion rate by the SCR member 60. The calculation of the NOX conversion rate by the SCR 60 member is made from the measured NOX level and a NOX level upstream of the SCR 60 member. The NOX level upstream of the SCR 60 member is SCR 60 member can be obtained using a dedicated sensor or using a NOX level model upstream of the organ of SCR 60. The NOX level upstream of the organ of SCR 60 is thus measured or estimated, and allows, with the NOX rate measured downstream, the calculation of the NOX conversion rate by the SCR member 60. Thus, a malfunction may correspond to a calculated conversion rate. NOx falling below a predetermined conversion threshold of failure. The default conversion rate threshold preferably depends on the temperature, Ti or T2, of the measurement of the NOx rate with which the conversion rate is calculated. The two preceding modes of correspondence between the measured NOX level and the operating insufficiency of the SCR member 60 may be implemented simultaneously by the proposed method. Thus, at a given temperature, the measured NOX level may not correspond to an operating failure of the SCR member 60 when: the predetermined NOX rate threshold of failure is not exceeded by the NOX level measured; and / or - the predetermined failure conversion rate threshold does not exceed the conversion rate calculated from the measured NOX level. In other words, the proposed method makes it possible to diagnose a failure of DOC 40 not directly via the reduction of treatment efficiency of HC and CO but indirectly via NOX emissions downstream of the SCR member. 60. [0039] Now, with reference to FIG. 1, a NOX sensor 64 downstream of the SCR is imposed by an onboard diagnostic computer for the reduction of NOX (not shown). The onboard diagnostic calculator of the reduction of NOX is an onboard diagnostic calculator, better known under the name of OBD calculator (abbreviation from the English expression on board diagnostics). The implementation of the method proposed by the same onboard computer does not generate the need for an additional sensor, unlike known solutions. Without the need for an additional sensor, the exhaust line 20, for which the proposed diagnostic process is applied, is then simpler. In addition, the use of NOx measurement downstream of the SCR member makes it possible to obtain a greater reliability of the proposed method compared to the diagnostic method based on an estimated model of the NOX level downstream of the reactor. SCR body. Ultimately, the invention makes it possible to obtain a reliable method for diagnosing the failure of an abatement member in an exhaust line, the remaining exhaust line being of simple design. The invention also relates to a motor vehicle. The motor vehicle then comprises the internal combustion engine 80, the exhaust line 20 of the internal combustion engine 80 and the diagnostic computer of the exhaust line 20, previously described. Referring to Figure 1, the exhaust line 20 also includes the sensor 64 of the NO rate. The computer advantageously implements the previously described diagnostic method. The implementation of the preceding diagnostic method for the exhaust line 20 is possible whereas the exhaust line 20 may not include a sensor, in particular no NO sensor, between the DOC 40 and the SCR device 60. The various measurements at Ti and T2 of the NO ratio can be carried out during different operating phases of the exhaust line 20 and the engine 80. Thus during a low or medium temperature operation phase , a first measurement of the rate of NO to Ti can be memorized by the computer. The second measurement of the rate of NO to T2 is performed when the exhaust line 20 and the motor 80 are in a high temperature operating phase. When the exhaust line 20 comprises at least one temperature sensor (not shown), the determinations of the operating phases at low or medium temperature and at high temperature can be carried out by measurement. At least one of the temperatures Ti and T2 then corresponds to a temperature measured by the temperature probe. It is preferred that the temperature sensor be present in the exhaust line for performing other functions than the failure diagnosis thus limiting the design costs of the exhaust line. When the exhaust line 20 is devoid of a temperature probe at the SCR member 60, at least one of the temperatures for which the measurements of the NO rate are made can be estimated rather than measured.

Thus, Ti and / or T2 then correspond to temperatures estimated at the time of the measurement of the level of NO downstream of the SCR member 60. The estimation is then carried out by a temperature model of the exhaust line 20 The temperature model used is advantageously based on at least one parameter of the parameter group consisting of: the engine speed 80; the torque of the motor 80; the fuel flow rate of the engine 80; the fuel phasing of the engine 80; the air flow rate of the engine 80, the recirculation rate in the engine 80 of the gases 90 to escape in the exhaust line 20; - the winnowing at the inlet of the engine 80; the speed of the vehicle comprising the engine 80 and the exhaust line 20; and the position of a turbocharger of the intake of the engine 80 recovering the kinetic energy of the gases 90 to escape in the exhaust line 20. Such a temperature model is then based on parameters at the level of the engine. motor 80 which are conventionally used by functions other than the failure diagnosis of the exhaust line 20. This allows for synergy, reducing the design costs and complexity of the engine 80, the line of exhaust 20 and the motor vehicle that includes them. In addition, this temperature model makes it possible to dispense with the presence of a temperature sensor specifically designed for measuring the temperature of the SCR member 60. The method proposed can also make it possible to determine the failure of the The SCR member 60 when, at T1 and T2, the measured nitrogen oxide levels both correspond to a failure of the SCR member to function. Indeed, in the case where it is the organ SCR 60 that is failing, the decrease in the efficiency of the treatment of NOX by the organ SCR 60 is substantial regardless of the temperature of the body SCR 60. [0049] In other words, the realization of the measurement of the NOX level at high temperatures (T2) where the SCR is independent of the NO2 / NOX ratio, then the correspondence or not of this measurement with a failure of The operation of the SCR member 60 makes it possible to remove the uncertainty. If the operating failure of the SCR member 60 is no longer determined at high temperatures (T2), then the SCR member 60 is operating properly and therefore DOC 40 is involved. If the operating failure of the SCR member 60 is still determined at high temperatures (T2), then the SCR member 60 is involved. Thus the failure of the SCR member 60 can be determined when the nitrogen oxide levels measured at T1 and T2, each exceed the predetermined thresholds of nitrogen oxides of T1 or T2 failure. The failure of the SCR member 60 can also be determined when the conversion rates of the NOs, calculated from the rates of NON measured at T1 and T2, each fall below the predetermined thresholds of predetermined conversion rates of failure at T1. or T2. The distinction of a defect due to the DOC 40 or due to the body of SCR 60 10 allows not having to change the two bodies in after-sales. The proposed method advantageously includes the signaling of the failure of the DOC 40 and / or the SCR 60 member. This signaling is then intended for the user of the vehicle comprising the exhaust line 20 or the user. of the internal combustion engine 80. The distinction of a defect due to DOC 40 or due to the SCR component 60 being able to be performed on the engine in operation, the signaling of the origin of the failure can be indicated directly to the user even before the passage in after-sales. After the determination of a decrease in the efficiency of the NO treatment by measuring the level of NO at the usual temperatures (Ti), it may be envisaged to improve the discrimination between the DOC 40 and the SCR 60. Thus, in the case where two temperature probes upstream and downstream of the DOC 40 are present in the exhaust line 20, the process may include the incrimination of the DOC 40 via the exotherm it generates. Indeed, during the aging of DOC 40 the exotherm it generates decreases. This decrease of the exotherm is visible in FIG. 5 which represents a graph comparing the evolution of the temperature difference between the upstream and the downstream of the DOC 40 for a new DOC (54) and an old DOC (56). ). The temperature difference curves 54 and 56 are obtained when the motor 80 undergoes a standard operating profile represented by the curve 58 corresponding to the speed of the vehicle comprising the engine 80. The incrimination of the DOC 40 via the exotherm which it is also possible by comparing the temperature rise rate of the DOC 40 with a predetermined reference temperature rise rate. The temperature increase rate of the DOC 40 decreases with the aging of the DOC 40. The incrimination of the DOC 40 by exotherm can also be provided in the case where a single temperature sensor is present in the exhaust line 20. In this case, it is advantageous to go to a known operating point to determine the decrease of the exotherm of DOC 40. In the case where temperature probes are also present in the exhaust line. 20, the method may also include incriminating DOC 40 using aging models of DOC 40. Such a model consists of recording the thermal seen by the SCR 60 organ and by DOC 40 at during the life of the vehicle. The defect can thus be attributed to the organ whose aging model is the most affected. This process may also include the incrimination of DOC 40 through the consumption of DOC 50 in 40. Indeed, during aging DOC 40, its oxygen consumption used to treat pollutants decreases. Such incrimination is possible when an O 2 probe is present in the exhaust line 20 upstream of the DOC 40. However, the NOX sensor 64 can also make it possible to know the oxygen concentration, especially if one is located. on a known operating point. With reference to FIG. 1, the exhaust line 20 may comprise a urea injector 62 upstream of the SCR member 60. Thus, the proposed method may also include urea injection upstream of the organ of SCR 60. Urea corresponds to a SCR reducer also known as AUS32.

Claims (10)

REVENDICATIONS1. A method for diagnosing failure of a member in an exhaust line (20) of gas (90) from an internal combustion engine (80), the exhaust line (20) comprising, in the sense of exhaust gas, an oxidation catalyst (40) and a selective catalytic reduction member (60), the method comprising: - measurements at a first temperature (Ti) and a second temperature (T2) of the rate of nitrogen oxides downstream of the selective catalytic reduction member (60) in the gas escape direction (90), the second temperature (T2) being higher than the first temperature (Ti); the method being characterized in that it comprises determining a failure of the oxidation catalyst (40) when: at the first temperature (Ti), the measured nitrogen oxide level corresponds to a failure of operation the selective catalytic reduction member (60); and that - at the second temperature (T2), the nitrogen oxide content measured does not correspond to an operating failure of the selective catalytic reduction member (60). 2. The diagnostic method according to claim 1, characterized in that at least one of the first and second temperatures (Ti, T2) is a temperature measured at the selective catalytic reduction member (60). The diagnostic method according to claim 1 or 2, characterized in that at least one of the first and second temperatures (Ti, T2) is an estimated temperature of the selective catalytic reduction member (60), estimate 25 being made by a temperature model of the exhaust line (20). The diagnostic method according to claim 3, characterized in that the temperature model is based on at least one parameter of the parameter group consisting of: - the engine speed (80); The torque of the motor (80); the fuel flow rate of the engine (80); - the fuel phasing of the engine (80); - the air flow of the engine (80) - the recirculation rate in the engine (80) of the gases (90) to escape in the exhaust line (20); - the winch on admission of the engine (80); the speed of a vehicle comprising the engine (80) and the exhaust line (20); and - the position of a turbocharger of the engine intake (80) recovering the kinetic energy of the gases (90) to escape in the exhaust line (20). 5. The diagnostic method according to any one of claims 1 to 4, characterized in that it comprises the determination of a failure of the selective catalytic reduction member (60) when, at the first temperature (Ti) and at the second temperature (T2), the nitrogen oxide levels measured correspond to an operating failure of the selective catalytic reduction member (60). 6. The method of diagnosis according to any one of claims 1 to 5, characterized in that, at least one of the first and second temperatures (Ti, T2), the measured nitrogen oxide level corresponds to insufficient functionality of the selective catalytic reduction member (60) when the measured nitrogen oxide content exceeds a predetermined nitrogen oxide threshold of failure. 7. The diagnostic method according to any one of claims 1 to 6, characterized in that, at least one of the first and second temperatures (Ti, T2), the method comprises calculating the conversion rate of the nitrogen oxides by the selective catalytic reduction member (60) from the nitrogen oxide content measured, the nitrogen oxide content measured at at least one of the first and second temperatures (Ti , T2) corresponding to insufficient functionality of the selective catalytic reduction member (60) when the calculated nitrogen oxide conversion rate falls below a predetermined failure conversion rate threshold. 8. The diagnostic method according to any one of claims 1 to 7, characterized in that: - the first temperature (Ti) is a normal operating temperature of the exhaust line (20) and is between 150 ° C and 300 ° C; and the second temperature (T2) is a high operating temperature of the exhaust line (20) and is greater than or equal to 300 ° C. 9. The diagnostic method according to any one of claims 1 to 8, characterized in that the internal combustion engine (80) from which the gases (90) to escape in the exhaust line (20) is a motor diesel. 10. A motor vehicle comprising an internal combustion engine (80), an exhaust line (20) of the gases (90) of the internal combustion engine (80) and a computer for diagnosing the failure of an organ of the line exhaust system (20), the exhaust line (20) comprising, in the gas exhaust direction (90), an oxidation catalyst (40), a selective catalytic reduction member (60), a sensor (64) nitrogen oxides content; the motor vehicle being characterized in that the computer implements the diagnostic method according to one of claims 1 to 9.