Page 160 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

142 Methods for Monitoring and Diagnosing the Efticiency of Catalytic Converters

b) an average value of the cumulative value of the difference
between two adjacent values of the air/fbel ratio control amount
over a predetermined time period
4) deterioration detection-inhibiting means for inhibiting detection of deterioration of the
catalytic converter when the amount in variation of the aidfirel ratio control amount exceeds
a predetermined value.

The catalytic converter deterioration detection of step 3 is camed out by making use of an
amount obtained by subtracting an amount ascribed to the amount of variation in the aidfuel
ratio control amount obtained by dividing the cumulative value of the difference between two
adjacent values of the air/fbel ratio control amount over the predetermined time period by an
integral term applied in the aidfbel ratio control, from an average value of the catalytic
converter deterioration parameter over the predetermined time period.

The patent disclosure US5678402 (1997) describes an air/fbel ratio control system for an
internal combustion engine and a device that can estimate the temperature of the catalytic
converter. The deterioration of the converter as well as the temperature of the converter are
used as parameters to set this air/fbel ratio control. The method comprises the following steps:
1) calculating a maximum oxygen storage amount indicative of the maximum amount of
oxygen that can be stored in the catalytic converter. This is based on at least one of
a) the temperature of the catalyst of the catalytic converter, or
b) a degree of deterioration of the catalytic converter
2) forcibly oscillating an aidfie1 ratio of a mixture supplied to the engine at a predetermined
frequency and a predetermined amplitude
3) changing at least one of the predetermined frequency and the predetermined amplitude at a
predetermined rate of change
4) setting the predetermined rate of change of the predetermined frequency and the
predetermined amplitude, in dependence on the maximum oxygen storage amount
calculated in step I.