Page 66 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

48 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

When one of these values is out of a predetermined range then the catalytic converter is
considered to be of low performance.

catalytic converter
A21 ;; ; deteriorated
slightly
b) t

I
cata lytic converter
deteriorated

TIME

Fig. 19 (from DE4 1 12478)

In DE4112479 (1992) the engine aidfuel ratio is forced to oscillate between a rich and a lean
value. The quotient of the measured downstream maximum 112 value over the upstream
maximum 11 value is used then as a deterioration variable AZ for determining the deterioration
of a catalytic converter.

The method then comprises correction of AZ based on values of the operating variables, in
order to reduce the influence of the operating conditions on AZ.