Catalytic Converter Monitoring

Catalytic Converter Monitoring

Catalyst monitoring is based on monitoring the oxygen storage capability. The (nonlinear) correlation between conversion efficiency and storage capability has been shown in various investigations. The engine mixture control results in regular Lambda oscillations of the exhaust gas (Lambda = normalized air fuel ratio). In case of using a UEGO-based Lambda control, Lambda oscillations are artificially created during catalyst monitoring. These oscillations are dampened by the storage activity of the catalyst. The amplitude of the remaining Lambda oscillations downstream the catalyst indicates the storage capability.

The procedure compares the signal amplitudes obtained from the downstream sensor to the modelled signal amplitudes. The modelled signal amplitudes are derived from the model of a borderline catalyst. In case the measured amplitudes exceed those of the model, the catalyst is considered as defective. This information is evaluated during one single engine load and speed range. According to the described operating principle the following main parts can be distinguished:
- Computation of the amplitude of the downstream Lambda sensor
- Modelling of a borderline catalyst and of the signal amplitudes of the downstream Lambda sensor
- Signal evaluation
- Fault processing
- Check of monitoring conditions