FR2914355A1 - METHOD AND DEVICE FOR DIAGNOSING AN EXHAUST GAS CLEANING SYSTEM - Google Patents

Abstract

A method of diagnosing a one or more stage exhaust gas cleaning plant (20) installed in at least one exhaust gas line (16, 17) of an internal combustion engine (10), according to at least one amount of gross exhaust gas (42, 47) of the engine (10) is determined. The conversion capacity of the various components of the exhaust cleaning system (20) is determined. at least a quantity of normal exhaust gas (42, 47), if appropriate, normalized and of the conversion capacity of the various components, an emission of exhaust gas is determined and compared with a predefined diagnostic threshold (45).

Description

Field of the Invention The present invention relates to a method of

  diagnosis of a single stage or multi stage exhaust gas cleaning installation installed in at least one exhaust pipe of an internal combustion engine, wherein at least a quantity of raw exhaust gas is determined of the motor. The invention also relates to a device for implementing such a method.

  STATE OF THE ART The oxygen storage capacity of an exhaust cleaning plant is used to receive the oxygen during the lean-mixture phases and to restore the oxygen again during the phases of the process. rich mixture. This makes it possible to convert the harmful oxidizable components of the exhaust gases. An exhaust gas sensor installed downstream of the exhaust cleaning system monitors the oxygen storage capacity of the exhaust cleaning system. This ability to accumulate oxygen must be monitored as part of an on-board diagnostic as it is a measure of the conversion capability of the exhaust cleaning system. In order to determine the oxygen storage capacity, the entire exhaust cleaning system is first charged with oxygen around a lean phase, and then during a single phase. rich mixture, the system is emptied with an exhaust gas whose lambda coefficient is known taking into account the flow rate of gas passage, or it is first empty of the oxygen of the gas cleaning system exhaust through a rich mixing phase and then during a lean phase is charged with exhaust gas having a known lambda coefficient taking into account the flow of exhaust gas passing. The lean phase ends when the exhaust gas sensor downstream of the exhaust cleaning plant detects oxygen that can no longer be accumulated by the exhaust cleaning system. Likewise, a rich phase is terminated when the exhaust gas sensor detects the passage of rich exhaust gas. The duration of the filling and evacuating phases with the amount of air passing through the internal combustion engine during each respective phase can be a measure of the oxygen storage capacity and thus the aging condition. of the exhaust cleaning system. DE-41 12 480-C2 discloses a method and a device for determining the aging state of a catalyst. For this, the catalyst is first loaded with oxygen during a lean phase and as soon as the oxygen-rich exhaust gas arrives downstream of the catalyst, it is switched to a rich phase. The diagnosis begins when the internal combustion engine is idling at this point. The rich phase is terminated when rich exhaust gases are detected downstream of the catalyst. During the duration of the rich phase, the amount of air passing through the internal combustion engine is determined. If during the duration of the rich phase the internal combustion engine is idle, the ratio of the duration of the rich phase and the quantity of air multiplied by a coefficient is used as a measure of the capacity to accumulate. oxygen and thus the aging state of the catalyst. The advantage of performing the process during an idle phase is that the duration of the rich phase is, for example, from 11 to 12 seconds and can thus be determined with greater precision than during the charging operation when the rich phase would for example have a duration of 0.5 seconds. For the measurement of aging, a threshold is set below which the catalyst is considered to have no longer sufficient conversion capacity. If the exhaust gas cleaning system of the internal combustion engine is equipped with several catalysts, according to the state of the art, the overall conversion capacity of the exhaust gas cleaning system is checked. For this purpose, a threshold corresponding to the minimum conversion capacity of a catalyst is switched to levels depending on whether the conversion capacity of a second catalyst is within or outside a predefined range. This process also applies by extension to a larger number of catalysts. The catalysts can be installed in series in an exhaust pipe or in parallel in several exhaust pipes.

  OBJECTS OF THE INVENTION The present invention aims to develop a method and a device for diagnosing an exhaust gas cleaning installation formed of several separate cleaning components installed in the exhaust gas duct. an internal combustion engine, allowing a reliable evaluation of the conversion capacity of the exhaust cleaning system. DESCRIPTION AND ADVANTAGES OF THE INVENTION The present invention relates to a process of the type defined above, characterized in that the conversion capacity of the various components of the exhaust gas cleaning system is determined, and from at least a quantity of normal exhaust gas, if any normalized and the conversion capacity of the various components, an emission of exhaust gas is determined and compared with a predefined diagnostic threshold.

  The method according to the invention makes it possible to reduce the number of exhaust gas cleaning installations which are judged to be defective and which nonetheless comply with the regulations. This reduces the maintenance and repair costs of a motor vehicle equipped with an internal combustion engine. At least a quantity of raw exhaust gas can be determined from a model of the behavior of the internal combustion engine under the operating conditions respectively existing or by proceeding by measurement. The diagnostic process is particularly simple and economical and at the same time it is sufficiently precise as the conversion capacity of the exhaust gas cleaning system of separate components installed in series in the direction of the exhaust gases by a multiplicative evaluation, and the exhaust emission of components installed in parallel is evaluated by an additive evaluation. If for each component of the exhaust cleaning system a measurement of aging is determined and if from the measurement of aging and with the aid of a characteristic curve the conversion capacity is determined, the process applies in a particularly simple way. If from the measurement of aging, using a field of characteristics taking into account the entry of the exhaust gases, it is determined the capacity of conversion of distinct components installed one behind the other, one can hold account of the non-linear character of the conversion capacity and this capacity can be determined in a particularly good way. As a measure of aging according to the state of the art, for example, the oxygen storage capacity in a catalyst is used. If the composition of the exhaust gas is determined between the separate components installed in series in the direction of passage of the exhaust gas in an exhaust pipe, the process can be simplified and in particular it can be determined more precisely. aging measurements and conversion capabilities of separate components installed in series in the direction of passage of the exhaust gases. A variant of the method for performing a particularly precise diagnosis of the exhaust gas cleaning system and with a particularly small number of errors in the diagnosis of exhaust gas cleaning installations, declared wrongly as defective, provides to separately form the measurement of aging of the conversion capacity of gaseous exhaust components limited by regulations such as hydrocarbons and nitrogen oxides. An advantageous variant of the method provides for the diagnosis of the exhaust gas cleaning installation on the basis of a diagnostic threshold determined beforehand by a test, and the quantity of exhaust gas supplied is compared with a diagnostic threshold. The diagnostic threshold is set in a check during a development phase. Similarly during the development phase a defined amount of raw exhaust gas is determined and a conversion defined by a verification as a reference point. This procedure reliably diagnoses an exhaust gas cleaning system that is defective. The problem posed by the invention in the context of the device is solved by a switching device for adaptation to each exhaust gas cleaning installation. The device according to the invention can be manufactured in a very large series as a standard component by means of this internal switching device and can be applied to exhaust gas cleaning plants comprising different catalyst devices. Drawings The present invention will be described hereinafter in more detail with the aid of an exemplary embodiment shown in the accompanying drawings in which: - Figure 1 is a schematic view of the technical environment in which the method of the invention; and Figure 2 shows a diagnostic system for an exhaust cleaning plant. DESCRIPTION OF EMBODIMENTS OF THE INVENTION FIG. 1 schematically shows the technical environment in which the method according to the invention applies to diagnose an exhaust gas cleaning system 20 with several ducts and / or several stages. . An internal combustion engine 10 receives combustion air by an air supply 11 and determines the mass of the air using a mass air flow meter 12. The mass air flow meter 12 can be realized as a mass flowmeter of hot film air. The air supply line 11 is furthermore equipped with a throttle flap 13. The exhaust gases of the internal combustion engine 10 are discharged through a first exhaust gas duct 16 and a second gas duct. exhaust 17; according to the direction of passage of the exhaust gas, downstream of the internal combustion engine 10, in the first exhaust pipe 16 there is a first lambda probe 31, a first pre-catalyst 21, a second lambda probe 32, a first main catalyst 23 and a third lambda probe 33. Downstream of the first main catalyst 23 exhaust gas is discharged through a first exhaust gas duct 18. In the second gas duct 17, according to the direction of passage of the exhaust gas, downstream of the internal combustion engine 10 there is a fourth lambda probe 34, a second pre-catalyst 22, a fourth lambda 35 probe, a second main catalyst 24 and a sixth lambda probe 36. After the second main catalyst 24, the exhaust gas is discharged through a second exhaust gas duct 19. A motor control 15 controls the internal combustion engine 10. This On the one hand, the controller supplies fuel to the internal combustion engine 10 via a fuel metering system 14 and controls the throttle flap 13 and on the other hand receives the signals from the mass air flow meter 12. The transmission lines 30 of the lambda probes transmit to the motor controller 15 the signals of the lambda probes 31, 32, 33, 34, 35, 36. According to one embodiment, the second lambda probe 32 and the fifth probe can be omitted. lambda 35. The first lambda probe 31 and the fourth lambda probe 34 determine a real value of the lambda coefficient of the air / fuel mixture supplying the internal combustion engine 10; these probes can be broadband probes. The lambda probes 32, 33, 35, 36 determine the composition of the exhaust gas after the pre-catalysts 21, 22 and the main catalysts 23, 24 and can be realized in the form of probes with sudden variation. Figure 2 schematically shows a diagnostic system 40 for evaluating the conversion capability of a multi-stage exhaust gas cleaning plant. With the aid of a first switching stage 63 and a second switching stage 66, the diagnostic system 40 can be adapted to the catalyst installation of any type of gas cleaning installation. 20. For the exhaust gas cleaning system 20 described in FIG. 1, with two pre-catalysts and two main catalysts, the first switching stage 63 is placed in the high position and the second switching stage 66 in the low position. For the first exhaust gas duct 16 described in FIG. 1, a first quantity of crude exhaust gas 42 is defined. In addition, a first aging measurement 43 is provided at a first characteristic field 51 and is operated in accordance with FIG. the instantaneous flow rate of the exhaust gas and, if appropriate, the exhaust gas component to be evaluated. Examples of exhaust gas components to be evaluated are hydrocarbons or nitrogen oxides. The output value of the first feature field 51 is applied with the first raw gas amount 42 to a first multiplier stage 61; in this stage the value of the exhaust gases is defined after the first pre-catalyst 21. The first multiplier stage 61 supplies the signal to the first switching stage 63; the latter being in its upper switching position, transmits this signal to a second multiplier stage 64. The second multiplier stage 64 further receives an aging measurement 44 evaluated by a second characteristic field 52 and representing the aging of the first main catalyst 23 according to FIG. 1. After the second multiplication stage 64, the signal, relative to the first exhaust gas duct 16, corresponds to a first exhaust gas value downstream of the main catalyst 72.

  For the second exhaust gas pipe 17 there is a corresponding part of the diagnostic system 40 which, starting from a second quantity of crude exhaust gas 47, of a third aging measurement 48 evaluated in a third field of characteristics 54 with a third stage multiplier 65, the second stage switch 66 and a fourth stage multiplier 67, defines a second value of exhaust gas downstream of the main catalyst 73 for the second exhaust pipe 17. The first the exhaust gas value downstream of the main catalyst 72 and the second exhaust gas value downstream of the main catalyst 73 are added in a second adder stage 68; the sum is compared in a comparison stage 69 to a diagnostic threshold 45. As a result, a diagnostic signal 70 indicates whether the conversion capability of the multi-level exhaust cleaning plant 20 is sufficient.

  If the exhaust cleaning system consists of two parallel-connected pre-catalysts and one main catalyst, the diagnostic system 40 is adapted to this embodiment in that a pre-selection signal Catalyst 41 switches the first switching stage 63 to its low switching position; thus the output signal of the first multiplier stage 61 and the output signal of the second switching stage 66 will be summed in a first adder stage 62. In the output signal of the second summation stage 68, account is thus taken of the exhaust of the two pre-catalysts.

  If the exhaust gas cleaning system comprises a pre-catalyst and a main catalyst, the diagnostic system 40 can be adapted; for this a switching signal 46 switches the second switching stage 66 to its upper switching position and thus connects the input of the second switching stage 66 to a zero value 53. Thus, at the output of the second switching stage 66 there will be also a zero value which after the fourth multiplication stage 67 gives a zero value. The output signal of the second adder stage 68 is thus equal to the first value of the exhaust gas after the main catalyst 72 and thus represents the first exhaust gas pipe 16. The diagnostic threshold 45 is thus adapted to any mode of the diagnostic system 40. The diagnostic system 40 may use several aging measurements for each component considered separately, for example for hydrocarbons and nitrogen oxides, or a frontal zone and for each exhaust gas component. by proceeding separately.35

Claims (7)

  1) A method for diagnosing a one or more stage exhaust gas cleaning plant (20) installed in at least one exhaust pipe (16, 17) of an internal combustion engine (10) , wherein at least a quantity of the raw exhaust gas (42,47) of the engine (10) is determined, characterized in that the conversion capacity of components separate from the gas cleaning plant is determined. exhaust (20), and from at least a quantity of normal exhaust gas (42, 47), if any, normalized and the conversion capacity of the separate components, an emission of exhaust gas is determined and compares to a predefined diagnostic threshold (45). 2) Process according to claim 1, characterized in that it is evaluated multiplicatively the conversion capacity of separate components installed in series in the direction of passage of the exhaust gas in the exhaust cleaning system ( 20), and the emission of exhaust gases from components installed in parallel is additionally evaluated. 3) Process according to claim 1, characterized in that for each separate component of the exhaust gas cleaning system (20) an aging measurement is determined, and from this measurement of aging is determined the capacity of conversion by means of a characteristic curve or a characteristic field taking into account the entry of the exhaust gases. 4) Method according to one of claims 1 to 3, characterized in that one determines the composition of the exhaust gas between different separate components installed in series in the direction of passage of the exhaust gas in at least one gas pipe exhaust (16, 17). 5) Process according to claim 1, characterized in that the measurement of aging is separately formed for the conversion capacity of gaseous components of exhaust gas, limited by the regulations such as hydrocarbons and nitrogen oxides. 6) Method according to claim 1, characterized in that the diagnosis of the exhaust gas cleaning system (20) is carried out on the basis of a diagnostic threshold determined beforehand by a verification, and compared the quantities of exhaust gas emitted at a diagnostic threshold. 7) Device for diagnosing a one or more stage exhaust gas cleaning plant (20) installed at least one exhaust gas line (16, 17) of an internal combustion engine (10), characterized by a communication device implementing a method according to one of claims 1 to 6, allowing adaptation to each exhaust gas cleaning installation (20).