GB2411008A

GB2411008A - Diagnostic process for condition of catalytic converter system

Info

Publication number: GB2411008A
Application number: GB0501898A
Authority: GB
Inventors: Axel Lang; Jorg Gunnewig
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 2004-02-12
Filing date: 2005-01-31
Publication date: 2005-08-17
Anticipated expiration: 2025-01-31
Also published as: DE102004006992B4; GB0501898D0; GB2411008B; DE102004006992A1

Abstract

The system has at least one pre-treatment device upstream of at least one main treatment device in an IC engine exhaust. The diagnostic process comprises: - <SL> <LI>a) determining a value for the conversion performance of at least one pre-treatment device (102), and comparing the value with a predetermined first limit value (104), <LI>b) producing a diagnostic result "exhaust gas treatment satisfactory" and terminating the diagnostic process if all the values determined in step a) for the conversion performance(s) reach or exceed the predetermined first limit value (108), IF at least one of the values determined in step a) falls below the first limit value; <LI>c), d) repeating steps a) and b) for at least one main treatment device and a predetermined second limit, (112), (114), 118), <LI>IF at least one of the values determined in step c) falls below the second limit value, OR IF no value could be determined for the conversion performance in step c); <LI>e), f) repeating steps a) and b) for the conversion performance of the whole exhaust treatment system and a predetermined third limit, (122), (124), 128), <LI>g) producing the diagnostic result "exhaust gas treatment system defective" and outputting a corresponding fault signal(132), if the value determine in step e) for the conversion performance of the whole exhaust treatment system lies below the predetermined third limit value. </SL>

Description

241 1 008 Diagnostic process for determining a condition of a catalytic

converter system The invention relates to a diagnostic process for determining the condition of a catalytic converter system in an exhaust gas train of an internal combustion engine.

Methods are known for diagnosing the condition of a catalytic converter of an internal combustion engine, which methods measure an oxygen storage capacity (OSC) of the catalytic converter by means of active lambda adjustment. This storage capacity correlates with the hydrocarbon (HC) conversion in the catalytic converter. When the catalytic converter has good conversion properties, the lambda fluctuations upstream of the catalytic converter, which are actively produced by the lambda controller and detected by a first lambda probe, are smoothed out by the oxygen storage capacity of the catalytic converter. If, as a result of aging, poisoning through leaded fuel or combustion misfires the catalytic converter has no conversion properties or only reduced conversion properties, the hunting existing upstream of the catalytic converter acts upon the lambda probe downstream of the catalytic converter. By comparing the signal amplitudes of the two lambda probes it is possible to conclude whether the catalytic converter is operational or defective, as known, for example from DE 23 28 459 Al or US 5 509 267. For diagnostic purposes the OSC is additionally correlated with light-off and conversion behaviour of the catalytic converter. In order to measure the OSC, oxygen, which may possibly be stored in the catalytic converter, is, for example, first removed by setting a rich lambda value of, for example, 0.95 to 0. 98, and oxygen is then introduced by setting a lambda value of for example 1.02 to 1.05 with a lean, oxygen-rich exhaust gas. In so doing, the OSC is measured by an oxygen balancing process. The emptying and filling of the catalytic converter with oxygen is determined and controlled by a jump in an output signal of a lambda probe connected downstream of the catalytic converter into the rich or into the lean condition.

Since 1994 the "CARB" (California Air Resource Board) in the USA has required an on board diagnostic (OBD) system for motor vehicles. This system is intended to alert the driver to operational faults on the vehicle which lead to exhaust gas limit values being exceeded. As a result, so-called "OBDII-diagnostics" have been produced which monitor all exhaust gas relevant components in the vehicle such as the catalytic converter, fuel system' lambda probe etc. for operation and plausibility. In order to ensure the acceptance of the OBD system with users, the CARB places great emphasis on the reliability of the system. At the same time this is also in the interest of the manufacturer since a 1 0-year guarantee must also be given against ODD faults so that erroneous diagnoses can lead to considerable costs, for example in the case of recall actions ordered by the state.

The document DE 196 20 417 C2 describes a diagnostic process for a catalytic converter system of an internal combustion engine with a plurality of catalytic converters, which are disposed one behind the other in an exhaust gas duct of the internal combustion engine, wherein, in dependence upon the operating state of the internal combustion engine one of the catalytic converters is subjected to a diagnosis. For this purpose the diagnostic regions of the different catalytic converters are allocated to different operating regions of the internal combustion engine. If the internal combustion engine is located in an operating region to which no diagnostic region of the catalytic converters is allocated, no diagnosis takes place.

The object of the invention is to improve the diagnosis of a catalytic converter system of an internal combustion engine with respect to cost and reliability.

This object is achieved in accordance with the invention by a diagnostic process of the type mentioned above with the features characterised in claim 1. Advantageous embodiments of the invention are described in the remaining claims.

For this purpose in the case of a diagnostic process of the type mentioned above the following steps are provided in accordance with the invention: (a) Determination of a value for the conversion performance of at least one of the pre catalytic converters and comparison of the value for the conversion performance with a predetermined first limit value; bl) Production of a diagnostic result "catalytic converter system satisfactory" and termination of the diagnostic process if all the values determined in step (a) for the conversion performance of the precatalytic converters reach or exceed the predetermined first limit value, or b2) Determination of a value for the conversion performance of the main catalytic converter and comparison of the value for the conversion performance of the main catalytic converter with a predetermined second limit value if at least one of the values determined in step (a) for the conversion performances of the pre-catalytic converters lies below the predetermined limit value; cl) Production ofthe diagnostic result "catalytic converter system satisfactory" arid termination of the diagnostic process if the value determined in step (b2) for the conversion performance of the main catalytic converter reaches or exceeds the predetermined second limit value, or (c2) Determination of a value for the conversion performance of the whole catalytic converter system and comparison of the value for the conversion performance of the whole catalytic converter system with a predetermined third limit value, if the value determined in step (b2) for the conversion performance of the main catalytic converter lies below the predetermined second limit value or in step (b2) no value could be determined for the conversion performance of the main catalytic converter; (dl) Production ofthe diagnostic result "catalytic converter system satisfactory" and termination of the diagnostic process if the value determined in step (c2) for the conversion performances of the whole catalytic converter system reaches or exceeds the predetermined third limit value, or (d2) Production of the diagnostic result "catalytic converter system defective" and outputting of a corresponding fault signal if the value determined in step (c2) for the conversion performances of the whole catalytic converter system lies below the predetermined third limit value.

This has the advantage that in order to evaluate the whole catalytic converter system the conversion performance of the whole catalytic converter system or a value representative of the conversion performance of the whole catalytic converter system does not necessarily have to be measured or determined, which can be disadvantageous with respect to pollutant emissions depending on the embodiment concerned.

In a preferred embodiment the main catalytic converter is an NOx storage catalytic converter and in step (b2) a value for the NOx lean conversion of the NOx storage catalytic converter is determined as a value for the conversion performance of the main catalytic converter.

Expediently in step (b2) a value for an NOx lean conversion of the NOx storage catalytic converter from a previous NOx lean diagnosis is used or, if there is no valid value for an NOx lean conversion of the NOx storage catalytic converter from a previous NOx lean diagnosis, a predetermined time period is allowed to elapse for a valid value for an NOx lean conversion of the NOx storage catalytic converter from an NOx lean diagnosis. Additionally it is advantageous that in step (b2) an NOx lean diagnosis is encountered if there is no valid value for an NOx lean conversion of the NOx storage catalytic converter from a previous NOx lean diagnosis and the internal combustion engine is in lean operation or such operation is possible.

In a particularly preferred development of the process in accordance with the invention in step (a) an oxygen storage capacity (OSC) is determined as a value for the conversion performance of the at least one pre-catalytic converter.

In step (c2) in a particularly preferred manner an oxygen storage capacity (OSC) of the whole catalytic converter system is determined as a value for the conversion performance of the whole catalytic converter system.

In order to satisfy the legal requirements for a so-called "on board diagnostic system" (OBD), for example a signal device, in particular a fault warning light, is activated in step (d2).

For example in step (b2) NOx storage efficiency is determined as a value for the NOx lean conversion.

The invention will be explained in more detail hereinunder with the aid of the drawing in which Fig. I shows a schematic block diagram of a preferred embodiment of the diagnostic process in accordance with the invention; Fig. 2 shows a schematic block diagram of an exemplified embodiment of an exhaust gas train of an internal combustion engine for implementation of the diagnostic process in accordance with the invention and Fig. 3 shows a schematic block diagram of an alternative embodiment of an exhaust gas train of an internal combustion engine for implementation of the diagnostic process in accordance with the invention.

Fig. 2 illustrates by way of example an embodiment of an exhaust gas train of an internal combustion engine having an engine block 10 and working cylinders 12, wherein the exhaust gas train downstream of the engine block 10 is divided into a first branch line 14 and a second branch line 16, which unite to form a common exhaust gas line 18. In the first branch line 14, as seen in the direction of flow, a first lambda probe 20 with a constant output signal, a first pre- catalytic converter 22 and a second lambda probe 24 with a binary output signal are disposed.

Optionally the respective first lambda probe downstream of the engine output can also be formed as a binary probe. In the second branch line 16, as seen in the direction of flow, a third lambda probe 26 with a constant output signal, a second pre-catalytic converter 28 and a fourth lambda probe 30 with a binary output signal are provided. The two branch lines 14 and 16 unite downstream of the second lambda probe 24 and the fourth lambda probe 30 to form a common exhaust gas line 18. In the common branch line 18, as seen in the direction of flow, a main catalytic converter 32, which is formed as an NOx storage catalytic converter, and an NOx sensor 34 are provided, which NOx sensor outputs an NOx signal and a binary lambda signal.

In Fig. 3 an alternative embodiment of an exhaust gas train of an internal combustion engine is illustrated, wherein functionally equivalent parts are designated with the same reference numerals as in Fig. 2 so that reference is made for explanation thereof to the description of Fig. 2 above. In contrast to the embodiment in Fig. 2 in the embodiment in accordance with Fig. 3 only a single exhaust gas line 18 is provided, in which, as seen in the direction of flow, the first lambda probe 20 having a constant output signal, the pre-catalytic converter 22, the second lambda probe 24 having a binary output signal, the main catalytic converter 32 and the NOx sensor 34, which outputs an NOx signal and a binary lambda signal, are provided.

In the arrangements illustrated in Figures 2 and 3 for an exhaust gas system it is possible to measure a condition of one of the catalytic converters of the whole catalytic converter system in isolation. Possible processes for this purpose are the so-called oxygen-based processes which determine the oxygen storage capacity (OSC) of the respective catalytic converter subsystem or catalytic converter. The OSC correlates with a damaging/aging condition of the catalytic converter and is therefore a value which represents the conversion performance of the catalytic converter. A defective component, i.e. catalytic converter, in terms of the OBD/FOBD (on board diagnostic system) must be indicated when, on the basis of the defective component, predetermined exhaust gas limit values or pollutant limit values are exceeded. If the pre- catalytic converter 22 or the pre-catalytic converters 22 and 28 is or are small in comparison with the total volume of all catalytic converters 22, 28, 32, for example 15 to 25% by volume, then, because of the assistance of the main catalytic converter in the conversion, the deterioration in the exhaust gas caused by damage to, or failure of the pre-catalytic converter(s) is not yet sufficient for a fault to be displayed in terms of the OBD.

Provision is thus made in accordance with the invention to determine the condition of the main catalytic converter in the event of damage to, or failure of at least one pre-catalytic converter for a further decision as to the possible fault indication in terms of the OBD. With respect to the main catalytic converter in the form of the NOx storage catalytic converter it is possible, from the value for the NOx lean conversion, to deduce the oxygen storage capacity (OSC) of the corresponding main catalytic converter and therefore to obtain a value which represents the 3- way conversion performance of the main catalytic converter. Use of the NOx storage condition or of the NOx lean conversion of the NOx storage catalytic converter as a value representative of the conversion performance offers the advantage that in order to evaluate the conversion performance of the whole catalytic converter system it is not fundamentally necessary to be presented with a measurement of the OSC of the whole catalytic converter system, which - depending on the embodiment - can be disadvantageous with respect to pollutant emissions.

A diagnostic process in accordance with the invention for the catalytic converter system in accordance with the embodiment of Fig. 2 is described by way of example hereinunder with the aid of the schematic block diagram of Fig. 1.

In a first step 102 the value for the OSC for each of the pre-catalytic converters 22 and 28 is determined separately. In a subsequent step 104 these values for the OSC for the respective pre catalytic converters are compared with a first predetermined limit value which, as appropriate, can also be selected to be different for each of the pre-catalytic converters. If the value for the OSC reaches or exceeds this first limit value the respective catalytic converter 22, 28 is evaluated as being "satisfactory". For the case where both catalytic converters 22 and 28 are evaluated as "satisfactory" the process passes via branch 106 to 108. In this step 108 the diagnostic result "catalytic converter system satisfactory" is produced and the diagnostic process is terminated. Inclusion of another examination result for a further catalytic converter, e.g. the main catalytic converter 32, is not carried out. Inclusion of a further examination result, e.g. of the OSC of the main catalytic converter 32, is not carried out. However, for this case it must be shown that, independently of the condition of the NOx storage catalytic converter 32, corresponding OBD threshold values are not reached. If at least one or if both of the pre catalytic converters 22 and 28 are classified as "defective" after the comparison in step 104, the process passes via branch 110 to step 112. In step 112 a value for an NOx lean conversion of the NOx storage catalytic converter is determined from a previous NOx lean diagnosis. If no current or valid result for an NOx lean conversion from an NOx lean diagnosis is present then, in the event of lean operation or if lean operation is possible, a minimum period of time is allowed to elapse in order to permit the NOx lean diagnosis to run. An NOx lean diagnosis is possibly encountered. In the following step 114 the value determined for the NOx lean conversion of the NOx storage catalytic converter is compared with a second predetermined limit value. If the main catalytic converter 32 is evaluated as "satisfactory" then the process passes via branch 116 to step 118. In step 118 the diagnostic result "catalytic converter system satisfactory" is produced and the diagnostic process is terminated. A further examination of, for example, an OSC of the whole catalytic converter system is not carried out. If the main catalytic converter 32 is classified as "defective" after the comparison in step 114, the process passes via branch 120 to step 122. In step 122 a measurement of the OSC over the whole catalytic converter system with the pre-catalytic converters 22 and 28 and the main catalytic converter 32 is requested. In a subsequent step 124 this value for the OSC of the whole catalytic converter system is compared with a third predetermined limit value. In the event that this value for the OSC of the whole catalytic converter system reaches or exceeds the third limit value, the whole catalytic converter system is evaluated as "satisfactory". In this case the process passes via branch 126 to a step 128. In step 128 the diagnostic result "catalytic converter system satisfactory" is produced and the diagnostic process is terminated. In the event that in a comparison in step 124 the OSC of the whole catalytic converter system does not equal the third limit value but fails to reach it, the whole catalytic converter system is evaluated as "defective".

In this case the process passes via branch 130 to step 132. In step 132 the diagnostic result "catalytic converter system defective" is produced. In accordance with the OBD requests a corresponding display device is activated in this case, e.g. a fault indicator light, which informs the driver of a motor vehicle that as a result of a defective component the prescribed pollution limit values are not being adhered to.

Claims

Tim! x. > }} ( CLAIMS

1 Diagnostic process for determining a condition of a catalytic converter system in an exhaust gas train of an internal combustion engine, wherein the catalytic converter system has at least one pre-catalytic converter and at least one main catalytic converter disposed in the exhaust gas train downstream of the pre-catalytie converter, comprising the following steps (a) Determination of a value for the conversion performance of at least one of the pre catalytic converters and comparison of the value for the conversion performance with a predetermined first limit value; bl) Production of a diagnostic result "catalytic converter system satisfactory" and termination of the diagnostic process if all the values determined in step (a) for the conversion performance of the precatalytic converters reach or exceed the predetermined first limit value, or b2) Determination of a value for the conversion performance of the main catalytic converter and comparison of the value for the conversion performance of the main catalytic converter with a predetermined second limit value if at least one of the values determined in step (a) for the conversion performances of the pre-catalytic converters lies below the predetermined first limit value; c I) Production of the diagnostic result "catalytic converter system satisfactory" and termination of the diagnostic process if the value determined in step (b2) for the conversion performance of the main catalytic converter reaches or exceeds the predetermined second limit value, or (c2) Determination of a value for the conversion performance of the whole catalytic converter system and comparison of the value for the conversion performance of the whole catalytic converter system with a predetermined third limit value, if the value determined in step (b2) for the conversion performance of the main catalytic converter lies below the predetermined second limit value or in step (b2) no value could be determined for the conversion performance of the main catalytic converter; (dl) Production ofthe diagnostic result "catalytic converter system satisfactory" and termination of the diagnostic process if the value determined in step (c2) for the conversion performances of the whole catalytic converter system reaches or exceeds the predetermined third limit value, or (d2) Production of the diagnostic result "catalytic converter system defective" and outputting of a corresponding fault signal if the value determined in step (c2) for the conversion performances of the whole catalytic converter system lies below the predetermined third limit value.

2 Process as claimed in claim 1, characterized in that the pre-catalytic converters are disposed in mutually parallel branches of the exhaust gas train.

3 Process as claimed in at least one of the preceding claims, characterized in that the main catalytic converter is an NOx storage catalytic converter and in step (b2) a value for the NOx lean conversion of the NOx storage catalytic converter is determined as a value for the conversion performance of the main catalytic converter.

4 Process as claimed in claim 3, characterized in that in step (b2) a value for an NOx lean conversion of the NOx storage catalytic converter from a previous NOx lean diagnosis is used or, if there is no valid value for an NOx lean conversion of the NOx storage catalytic converter from a previous NOx lean diagnosis, a predetermined time period is allowed to elapse tor a valid value for an NOx lean conversion of the NOx storage catalytic converter from an NOx lean diagnosis.

Process as claimed in at least one of claims 3 or 4, characterized in that in step (b2) an NOx lean diagnosis is encountered if there is no valid value for an NOx lean conversion of the NOx storage catalytic converter from a previous NOx lean diagnosis and the internal combustion engine is in lean operation or such operation is possible.

6 Process as claimed in at least one of claims 3 to 5, characterized in that in step (b2) NOx storage efficiency is determined as a value for the NOx lean conversion.

7 Process as claimed in at least one of the preceding claims, characterized in that in step (a) an oxygen storage capacity (OSC) is determined as a value for the conversion performance of the at least one pre-catalytic converter.

8 Process as claimed in at least one of the preceding claims, characterised in that in step (c2) an oxygen storage capacity (OSC) of the whole catalytic converter system is determined as a value for the conversion performance of the whole catalytic converter system.

9 Process as claimed in at least one of the preceding claims, characteriscd in that a signal device, in particular a fault warning light, is activated in step (d2).

10. Process as claimed in any preceding claim, wherein the internal combustion engine is an Otto engine or a diesel engine.

1 1. Process as claimed in any preceding claim, wherein the internal combustion engine has direct injection.

12. Process as claimed in any preceding claim, wherein the internal combustion engine is the engine of a motor vehicle.