Page 74 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

56 Methods for Monitoring and Diagnosing the Eficiency of Catalytic Converters

t

Fig. 25 (fiom DE421 11 16)

In DE4211116 (1993), at a certain time to a number of oscillations of the engine aidfitel ratio
takes place from rich to lean and the opposite. The mean value of the variation is maintained
constant, while the amplitude of the variation increases (fig. 25a). The corresponding voltage
indication VI of the upstream sensor is shown in fig. 25b, while the corresponding voltage
indications VZ of the downstream sensor for a non-efficient and for an efficient converter are
shown in figs. 25c and d respectively. The time tl at which simultaneously the upper peak of
the VZ variation passes over an upper predefined threshold value and the lower peak of the
V2 variation passes under a lower predefined threshold EZ is considered to be the degradation
criterion of a catalytic converter. The smaller the oxygen storage capability of the catalytic
converter the earlier point tl appears.

Patent application DE4323243 (1995) refers to a need-based method of heating a catalytic
converter. The converting power of the catalytic converter is determined by means of the two