Catalyst Monitoring

Catalyst Monitoring

Diagnostic Overview:
The diagnostic function which is used for monitoring of the catalyst efficiency is based on measure of the Oxygen within the catalyst determined by two Oxygen sensors. The results can be correlated between Oxygen / Hydrocarbon and Oxygen/ Oxides of Nitrogen.

General description
The method compares the signal amplitudes obtained from the downstream sensor to modeled signal amplitudes. The modeled signal amplitudes are derived from a borderline catalyst. The data for borderline catalysts are taken from measurement results on real life deteriorated catalysts. In case the measured amplitudes exceed those of the model, the catalyst is considered defective. This information is evaluated within one single air mass flow range.

According to the described operating principle the following main parts can be distinguished:

Computation of the amplitude of the downstream oxygen sensor
The amplitude of the signal oscillations of oxygen sensor downstream catalyst is calculated. This is accomplished by extracting the oscillating signal component, computing the absolute value and averaging over time.

Modeling of a borderline catalyst and of the signal amplitudes of the downstream oxygen sensor
The model is simulating the oxygen storage capability of a borderline catalyst. The signal of the downstream oxygen sensor is simulated in the catalyst model based on real time engine operating data (e.g. A/F ratio and engine load). The amplitude of the modeled signal oscillations is calculated.

Signal and fault evaluation
The signal amplitudes of the downstream oxygen sensor are compared with the model for a given time. In case of the signal amplitudes of the downstream sensor exceed the modeled amplitudes, the oxygen storage capability of the catalyst falls short of the borderline catalyst model.

Check of monitoring conditions
It is necessary to check the driving conditions for exceptions where no regular Lambda control is possible, e.g. fuel cut-off. During these exceptions, and for a certain time afterwards, the computation of the amplitude values and the post processing is halted. Thus, a distortion of the monitoring information is avoided.

Monitoring Structure
The catalyst temperature (model) activates the catalyst monitoring function if the catalyst temperature is above a predetermined value.

Flow Chart Catalyst Monitoring