Page 97 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Ford Motor Co - Ford France SA - Ford Werke AG - Ford Motor Co. Ltd. 79

The method of patent US5544481 (1996) comprises the following steps:
1) delivering fuel to the engine in proportion to a fuel signal
2) adjusting the fuel signal with a feedback variable derived from a comparison of a reference
amplitude to an output amplitude of the upstream exhaust gas oxygen sensor
3) biasing the fuel signal in relation to a biasing signal derived from a comparison of a
reference value to an output amplitude of the downstream exhaust gas oxygen sensor
4) generating a difference in amplitude of the downstream sensor output amplitude between
two successive sample periods
5) storing the downstream sensor output amplitude as a peak amplitude each sample period
when the downstream sensor amplitude difference changes signs thereby providing a stored
peak value
6) indicating a downstream sensor transition when the downstream sensor difference between
the stored peak value and the peak value stored during a previous change in said sign of the
downstream sensor amplitude exceeds a predetermined value
7) indicating catalytic converter efficiency from a ratio of transitions of the downstream
sensor transitions to transitions of the upstream signal derived from the upstream sensor
output amplitude

fuel tank
9

inducted
auxiliary catalyst air flow

Fig. 37 (from USS522219)