Catalyst Monitoring

GENERAL DESCRIPTION

Catalyst monitoring is based on monitoring its oxygen storage capability.

The engine closed loop feedback control generates lambda (air/fuel ratio) oscillations in the exhaust gas. These oscillations are dampened by the oxygen storage activity of the catalyst. The amplitude of the remaining lambda oscillations downstream of the catalyst indicates the storage capability.

MONITORING PROCEDURE

In order to determine the catalysts efficiency a fixed number of complete lambda controller cycles (oxygen oscillation from upstream sensor) are used to calculate the areas which are enclosed by the controller cycle curve and is also calculated mean value. The average of all areas displays the magnitude of the oxygen admission to the catalytic converter.





Lambda controller upstream catalyst

The magnitude of the oxygen admission is used to calculate the maximum permissible oscillation (areas of the cycle) of the downstream sensor of a still good working catalyst.





Downstream catalyst

Now the original measured oscillation (average of areas) from downstream sensor is compared to the calculated maximum permissible value.

A fault is detected if the quotient (measured to calculated value) is greater than a fixed number.





CATALYST MONITORING STRUCTURE