Method for determining the conversion performance of an oxygen storage-capable catalytic converter of an internal combustion engine

Abstract

In a method for determining the conversion performance of an oxygen storage-capable catalytic converter of an internal combustion engine, it is proposed that the catalytic converter be supplied with a stoichiometric exhaust gas composition, a known emission change is briefly undertaken and at the same time the signals of a lambda probe located downstream from the catalytic converter are detected so that based on the emission change and signals of the lambda probe a differentiated conclusion about the conversion performance of the catalytic converter for the pollutants hydrocarbon HC and nitrogen oxides NOx is delivered. According to the invention a simple and cost-effective method for differentiation of the pollutants hydrocarbon HC and nitrogen oxides NOx and thus for carrying out an improved diagnosis method is made available.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be detailed with reference to the following figure.

FIG. 1 is a graph illustrating the lambda value λ_upstream, λ_downstream upstream and downstream from a catalytic converter to be diagnosed over time t for the conversion performances of hydrocarbon HC and nitrogen oxides NOx.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

To carry out the proposed method, the catalytic converter is supplied with a stoichiometric exhaust gas composition so that a first lambda probe which is optionally connected upstream from the catalytic converter would display a lambda value λ_upstream=1.0. Alternatively this lambda value could also be obtained from a model computation including various operating parameters of the internal combustion engine.

If the catalytic converter is a new catalytic converter which ideally has a uniform conversion performance of about 99.9% among other things for hydrocarbon HC and nitrogen oxides NOx, 0.1% of the pollutants would arrive downstream from the catalytic converter. This means that the exhaust gas composition downstream from the catalytic converter would likewise be stoichiometric and that a second lambda probe connected downstream from the catalytic converter would likewise display a lambda value λ_downstream=1.0.

In the case, in which the catalytic converter is no longer new or the catalytic converter has nonuniform conversion for the arriving pollutants, that is, for example conversion of 99.8% for nitrogen oxides NOx and conversion of 99.9% for the other pollutants, downstream from the catalytic converter 0.2% of the nitrogen oxides NOx and 0.1% of the other pollutants are established. On the basis of this composition the lambda probe connected downstream from the catalytic converter would display a lambda value λ_downstream>1.0. This corresponds to a minor change to a richer mixture.

Conversely, in the case in which the catalytic converter has conversion for the hydrocarbon HC of 99.8% and conversion of 99.9% for the other pollutants, in which downstream from the catalytic converter 0.2% of the hydrocarbon HC and 0.1% of the other pollutants are established. And on the basis of this composition the lambda probe connected downstream from the catalytic converter displays a lambda value λ_downstream<1.0. This corresponds to a minor change to a leaner mixture.

So that this effect is intensified, i.e., can be more clearly measured and exceeds given threshold values, at this point upstream from the catalytic converter at time to a change of the emissions is effected. But by changing the emissions matching of lambda is necessary to continue to supply the catalytic converter with a stoichiometric exhaust gas composition.

If for example the proportion of nitrogen oxides NOx is increased as the change of emissions, the lambda probe connected downstream from the catalytic converter with nonuniform conversion shows a very distinct change of the voltage signal. With degraded conversion for nitrogen oxides NOx a clearly richer state is established so that the lambda probe indicates a lambda value λ_downstream>1.0. And with degraded conversion for hydrocarbons HC a clear leaning is established so that the lambda probe indicates a lambda value λ_downstream<1.0.

If conversely the proportion of the hydrocarbon HC is increased, the lambda probe connected downstream from the catalytic converter likewise shows a distinct signal change. Thus with degraded conversion for nitrogen oxides NOx a clearly richer state is established, that is, a lambda value λ_downstream<1.0 and with degraded conversion for hydrocarbons HC a clear leaning is established, that is, a lambda value λ_downstream>1.0.

Thus differentiated determination of the conversion performance for the hydrocarbons HC which are formed in oxidation and for the nitrogen oxides NOx which are formed in reduction can be undertaken from the known change of emissions and from the change of the lambda signal Δλ of the lambda probe connected downstream from the catalytic converter.

The degree of the respective conversion performance can also be determined from the emission change upstream and the lambda change Δλ downstream from the catalytic converter. And this degree of the respective conversion performance can be compared to the given maximum allowable boundary values.

Claims

1. Method for determining the conversion performance of an oxygen storage-capable catalytic converter of an internal combustion engine, wherein the catalytic converter is supplied with a stoichiometric exhaust gas composition, a known emission change being briefly undertaken upstream from the catalytic converter and at the same time the signals of a lambda probe located downstream from the catalytic converter being detected so that based on the emission change and signals of the lambda probe a differentiated conclusion about the conversion performance of the catalytic converter for the pollutants hydrocarbon HC and nitrogen oxides NOx is delivered.

2. The method according to claim 1, wherein when the signal of the lambda probe remains constant, uniform conversion performances of the catalytic converter for pollutants hydrocarbon HC and nitrogen oxides NOx are assumed.

3. The method according to claim 1, wherein when a sudden signal change occurs, nonuniform conversion performances of the catalytic converter for the pollutants hydrocarbon HC and nitrogen oxides NOx are assumed, a positive value of the signal change which corresponds to leaning of the exhaust gas composition indicating better conversion of the hydrocarbon HC than the nitrogen oxides NOx, and a negative value of the signal change which corresponds to greater richness of the exhaust gas composition indicating poorer conversion of the hydrocarbon HC than the nitrogen oxides NOx.

4. The method according to claim 3, wherein the respective degree of conversion of the hydrocarbon HC and the nitrogen oxides NOx is derived from the value of the signal change.

5. The method according to claim 1 wherein the known change of emissions upstream from the catalytic converter is achieved by turning the exhaust gas recirculation on or off.

6. A method of determining the performance of a catalytic converter of an internal combustion engine, comprising: supplying said catalytic converter with an exhaust gas sample of a known composition;detecting the lambda value of said sample downstream of said catalytic converter; anddetermining the differentiation of said detected lambda value and a selected lambda value.

7. A method according to claim 6 wherein said selected lambda value is derived from a model exhaust gas composition of said engine predicated on certain parameters thereof.

8. A method according to claim 6 wherein said selected lambda value comprises the lambda value of an exhaust gas of a stoichiometric composition.