Method for Diagnosing an Exhaust Gas Catalytic Converter and/or an Exhaust Gas Sensor of a Motor Vehicle Internal Combustion Engine

Abstract

A method for diagnosing an exhaust gas catalytic convertor and / or an exhaust gas sensor arranged downstream and / or upstream of the exhaust gas catalytic convertor in an exhaust gas system of a motor vehicle internal combustion engine. The internal combustion engine is operated with an air / fuel mixture having a substoichiometric air / fuel ratio. The internal combustion engine is switched off and an unfired towed operation with disabled fuel supply is performed in which air drawn in by the internal combustion engine is conveyed through the exhaust gas system to the exhaust gas catalytic convertor and exhaust gas sensor. The internal combustion engine is then operated with a substoichiometric air / fuel ratio and a signal of the exhaust gas sensor is evaluated with regard to a predefinable evaluation criterion, the signal being provided at least in a period of time between switch-off and the subsequent self-running of the internal combustion engine.

Description

BACKGROUND AND SUMMARY OF THE INVENTION[0001]Exemplary embodiments of the present invention relate to a method for diagnosing an exhaust gas catalytic convertor and / or an exhaust gas sensor arranged downstream and / or upstream of the exhaust gas catalytic convertor in an exhaust gas system of a motor vehicle internal combustion engine, with which a signal of the exhaust gas sensor is evaluated with regard to a predefinable evaluation criterion.[0002]A large number of methods have already been proposed for diagnosis of three-way catalytic convertors with oxygen storage capability, with which the effect of a sudden change in the air / fuel ratio during operation of a motor vehicle internal combustion engine is evaluated with regard to various signal parameters of an exhaust gas probe arranged in particular behind the catalytic convertor.[0003]For example, German Patent Document DE 10 2006 010 769 A1 discloses making a sudden change from engine operation with a leaner air / fuel ratio to en...

AI Technical Summary

Benefits of technology

The present invention provides a method for diagnosing an exhaust gas catalytic convertor and / or an exhaust gas sensor in a motor vehicle internal combustion engine with low harmful emissions during certain operating phases. The method involves operating the engine with a low air / fuel ratio and disabling fuel supply during towed operation or start-stop operation, resulting in low harmful emissions. The method can also be performed during natural operation of the engine with a highly reducing air / fuel mixture. The technical effect of the invention is to provide a reliable and efficient means for diagnosing exhaust gas catalytic convertors and sensors with low harmful emissions.

Problems solved by technology

Disadvantages with these methods include the fact that an exhaust gas purification capacity of the exhaust gas catalytic convertor is typically reduced both during the period of lean operation and during the period of rich operation and the fact that harmful substances enter the surrounding environment in unconverted form.

A sudden change to the air / fuel ratio is often also caused by transition into or from overrun operation.

A drawback here is that overrun operation is often undesirable or cannot be represented.

If, as is preferable, the internal combustion engine is operated before and after stoppage thereof with a merely slightly substoichiometric air / fuel ratio, the harmful emission is thus also low in these operating phases.

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