METHOD FOR OPERATING AN EXHAUST GAS AFTERTREATMENT SYSTEM OF AN INTERNAL COMBUSTION ENGINE WHICH HAS A THREE-WAY PRE-CATALYTIC CONVERTER AND EXHAUST GAS AFTERTREATMENT SYSTEM

Abstract

A method for operating an exhaust gas aftertreatment system of an internal combustion engine and an exhaust gas aftertreatment system are described. The internal combustion engine has a turbine wheel, which is arranged in the exhaust gas line, of an exhaust gas turbocharger, and a bypass line which bypasses the turbine wheel and in which a three-way pre-catalytic converter is arranged. A three-way main catalytic converter is situated in the exhaust gas line. A NOx sensor is provided which measures the NOx fraction in the exhaust gas downstream of the three-way pre-catalytic converter. If the measured NOx fraction exceeds a threshold value, the three-way pre-catalytic converter is diagnosed as faulty.

Claims

1. A method for operating an exhaust gas aftertreatment system of an internal combustion engine which has an exhaust gas line, a turbine wheel, arranged in the exhaust gas line, of an exhaust gas turbocharger, a bypass line, bypassing the turbine wheel and having a bypass valve, a three-way pre-catalytic converter arranged in the bypass line, and a three-way main catalytic converter arranged in the exhaust gas line, the method comprising: providing a NOx sensor in the bypass or exhaust gas line downstream of the three-way pre-catalytic converter and upstream or downstream of the three-way main catalytic converter; measuring NOx emissions in the exhaust gas by the NOx sensor; and diagnosing the three-way pre-catalytic converter as faulty if the measured NOx emissions lie above a threshold value.

2. The method as claimed in claim 1, wherein the NOx emissions and a lambda value are measured by the NOx sensor.

3. The method as claimed in claim 2, wherein after a defined time period for lighting-off of the three-way pre-catalytic converter, the lambda value is measured downstream of the three-way pre-catalytic converter and, at a lambda value in the range of 1, the NOx emissions are measured and the diagnosis of the three-way pre-catalytic converter is carried out.

4. The method as claimed in claim 1, wherein the measurements are carried out during a heating-up phase of the three-way pre-catalytic converter.

5. The method as claimed in claim 1, wherein total NOx emissions are calculated from the measured NOx emissions by integration of a NOx concentration with respect to an air mass flow.

6. An exhaust gas aftertreatment system of an internal combustion engine, the exhaust gas aftertreatment system comprising: an exhaust gas line; a turbine wheel is arranged in the exhaust gas line of an exhaust gas turbocharger; a bypass line bypassing the turbine wheel and having a bypass valve; a three-way pre-catalytic converter arranged in the bypass line; a three-way main catalytic converter arranged in the exhaust gas line; and a NOx sensor is arranged in the bypass or exhaust gas line downstream of the three-way pre-catalytic converter and upstream or downstream of the three-way main catalytic converter.

7. The exhaust gas aftertreatment system as claimed in claim 6, wherein the exhaust gas aftertreatment system is configured to execute a method comprising: measuring, at the NOx sensor, NOx emissions in the exhaust gas; and diagnosing the three-way pre-catalytic converter as faulty if the measured NOx emissions lie above a threshold value.

8. The exhaust gas aftertreatment system as claimed in claim 7, wherein the NOx sensor measures the NOx emissions and a lambda value.

9. The exhaust gas aftertreatment system as claimed in claim 8, wherein after a defined time period for lighting-off of the three-way pre-catalytic converter, the lambda value is measured downstream of the three-way pre-catalytic converter and, at a lambda value in the range of 1, the NOx emissions are measured and the diagnosis of the three-way pre-catalytic converter is carried out.

10. The exhaust gas aftertreatment system as claimed in claim 8, wherein the measurements are carried out during a heating-up phase of the three-way pre-catalytic converter.

11. The exhaust gas aftertreatment system as claimed in claim 8, wherein total NOx emissions are calculated from the measured NOx emissions by integration of a NOx concentration with respect to an air mass flow.

Description

DESCRIPTION OF DRAWINGS

[0017] FIG. 1 shows a schematic illustration of an exhaust gas aftertreatment system of an internal combustion engine; and

[0018] FIG. 2 shows a schematic enlarged illustration of part of the exhaust gas aftertreatment system of FIG. 1.

[0019] Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

[0020] The internal combustion engine schematically illustrated in FIG. 1 is a gasoline engine which has a standard air supply tract 3 and exhaust gas tract with an exhaust gas line 2. The internal combustion engine 1 is provided with an exhaust gas turbocharger which has a turbine wheel 5 which is arranged in the exhaust gas line 2.

[0021] As illustrated in FIG. 2, this turbine wheel 5 is bypassed by a bypass line 6 in which a three-way pre-catalytic converter 7 is situated. The exhaust gas flow is controlled via a bypass valve 9 in such a way that it either passes through the turbine wheel 5 via the exhaust gas line 2 or flows through the bypass line 6.

[0022] A three-way main catalytic converter 4 is situated downstream of the bypass line 6 in the exhaust gas line 2 and carries out corresponding exhaust gas purification in a known manner. As shown in FIG. 1, a NOx sensor 8 is arranged upstream or downstream of the three-way main catalytic converter 4. In FIG. 2, this sensor 8 is here shown only upstream of the three-way main catalytic converter 4.

[0023] The NOx sensor 8 diagnoses the three-way pre-catalytic converter 7 arranged in the bypass line 6. The functionality of this catalytic converter is checked thereby. This occurs by virtue of the fact that, with the aid of the NOx sensor 8, the NOx fraction in the exhaust gas is measured downstream of the three-way pre-catalytic converter 7 and the lambda value of the exhaust gas is measured downstream of the three-way pre-catalytic converter 7. Specifically, the procedure followed here is as follows:

[0024] Function checking of the three-way pre-catalytic converter 7 occurs during its heating-up phase. Following the starting of the engine and after expiry of a certain time period, for example of 10 sec, for reaching the light-off temperature of the three-way pre-catalytic converter 7, the lambda value and the NOx fraction in the exhaust gas are measured by the NOx sensor 8 downstream of the three-way pre-catalytic converter 7. The evaluation of the NOx fraction is carried out at a lambda value of 1 (sensor voltage at 650-750 mV). If the measured NOx emissions in the exhaust gas lie above a defined threshold value, for example above 100 ppm in dependence on or as a function of the air mass flow, the three-way pre-catalytic converter 7 is classified as faulty. If the NOx fraction lies below this threshold value, the three-way pre-catalytic converter 7 is considered to be functional.

[0025] A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.

LIST OF REFERENCE SIGNS

[0026] 1 Internal combustion engine [0027] 2 Exhaust gas line [0028] 3 Air supply tract [0029] 4 Three-way main catalytic converter [0030] 5 Turbine wheel [0031] 6 Bypass line [0032] 7 Three-way pre-catalytic converter [0033] 8 NOx sensor [0034] 9 Bypass valve