Page 204 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

186 Methods for Monitoring and Diagnosing the Eficiency of Catalytic Converters

6) measuring the upstream and downstream signal voltage states (VI, V2) within the
predetermined operation time in accordance with the upstream and downstream voltage
signals, thereby calculating a voltage ratio Y

where:
k number of periods of upstream signal inversions within said predetermined operating
time
7) calculating a deterioration measured value AZ of the catalytic converter based on the
calculated ratios of steps 4 to 6

AZ=AXNXX, XVXX,,

where
x, : correction factor for N as weight addition,
x,, : correction factor for C'as weight addition,
8) comparing the deterioration measured value AZ to a deterioration determining value, the
latter being set for each engine load.

In US5531069 (1996), it is first judged whether or not the catalytic converter is in a
predetermined warm-up state in relation to any engine load of the internal combustion engine.
The determination of the catalytic converter deterioration then takes place only when
predetermined deterioration-determining conditions are fklfilled. The judgment of deterioration
is determined by examining the output signals of the upstream and downstream oxygen
sensors, as in any of the previous mentioned methods.

The method of JP9096237 (1997) inhibits the deterioration detection of the catalytic converter
when the engine load is less than a lower limit value after correcting it with the atmospheric
pressure. The feedback control of the engine airhe1 ratio is based on both output signal of the
upstream or the downstream oxygen sensor

Other methods presented by Suzuki Motor Corp. are described in JP6229309 (1994),
JP7019033 (1995), 337197807 (1995) and JP8326525 (1996).