Page 100 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

82 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

1) adjusting the fuel delivered to the left bank of cylinders in response to the upstream sensor
placed at the right exhaust branch and in response to the oxygen sensor placed downstream
of the catalytic converter
2) adjusting the fuel delivered to the right bank of cylinders in response to the upstream sensor
placed at the left exhaust branch and in response to the oxygen sensor placed downstream
of the catalytic converter
3) creating an inferred signal by combining output signals from said left and right exhaust
oxygen sensors. An inferred signal is an inference of an output from a hypothetical exhaust
gas oxygen sensor exposed to a hypothetical blended mixture of exhaust gases from the
right and left exhaust manifolds. The inferred signal is extracted from a lookup table in
fbnction of the sampled signals of the left and right oxygen sensors
4) indicating converter efficiency in response to a ratio of a count in transitions between output
states of the downstream sensor to the count in transitions between output states of said
inferred signal. When this ratio exceeds a predetermined one the catalytic converter is
considered as degraded
The creation of the inferred signal and indication of the catalytic converter efficiency occur
during a test period, which is completed when the engine has completed operation within each
of a plurality of inducted air flow ranges for at least a minimum duration in each of said air
flow ranges. The minimum duration is determined when the inferred signal has completed a
predetermined number of transitions.

The table of inferred signals of step 3 is generated by empirical testing and measurements for
many combinations of catalytic converter upstream signals.