Page 133 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Toyota Motor Co. Ltd. 115

b) the lengths of the output signal of the downstream sensor, or
c) the lengths and areas of the output signal response curves of the
upstream and downstream oxygen sensor.

The use of a spontaneous synchronization instead of a forced one has the big advantage of not
provoking extra pollution to the atmosphere.

The method of US5377484 (1995) comprises the steps:
I) estimating the airhel ratio of a mixture of the exhaust gases from the individual exhaust
passages flowing into the common exhaust passage based on the output signals of the
upstream sensors. The estimation step comprises:
a) calculating a mean value of the air/fbel ratio of the exhaust gases
detected at the same time by the upstream sensors and determining
that said mean value is the airlfiel ratio of the mixture of the exhaust
gases, or
b) calculating a mean value of the aidfuel ratios detected by the
upstream sensors at a predetermined interval, and determining that
said mean value is the air/hel ratio of the mixture of the exhaust
gases.
2) determining whether or not the three-way catalytic converter has deteriorated based on the
output signal of the downstream air/f%el sensor and the estimated airhel ratio of the
mixture of the exhaust gases flowing into the common exhaust passage. The method of
EP0547326 (1993) is then used to determine the condition of the catalytic converter, where
the measured aidfie1 ratio of the upstream sensor is replaced by the estimated airhe1 ratio
of the mixture of the exhaust gases from the individual exhaust passages flowing into the
common exhaust passage. Ratios of lengths and bounded areas of the downstream signal to
the estimated upstream signal are calculated and depending on the relationship of these
ratios, conclusions are drawn about the condition of the catalytic converter.