Page 214 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

I96 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

upstream
sensor
voltage

now deteriorated

sensor
voltage

-
_._ 1
-'L
converter

Fig. 88 (from US5591905)

The method of US5640846 (1997) presents an improved control of the engine aidfuel ratio to
diagnose accurately the catalytic converter efficiency. The method comprises the following
steps:
I) detecting the upstream concentration of a particular component of the exhaust gas to output
a first aidfuel ratio signal indicating the upstream concentration
2) detecting the downstream concentration of the particular component of the exhaust gas to
thereby output a second aidfuel ratio signal indicating the downstream concentration
3) controlling a target aidfuel ratio of a mixture supplied to the engine by arithmetically
determining a target aidfuel ratio control quantity on the basis of the first and second aidfuel
ratio signals. The control of the engine aidfuel ratio comprises the following steps:
a) determining a first aidfuel ratio control quantity on the basis of the first aidfbel ratio
signal
b) determining a second aidfuel ratio control quantity on the basis of the second aidhe1
ratio signal
c) correcting the first air/fbel ratio control quantity with the second air/%el ratio control
quantity to thereby determine the target air/fbel ratio control quantity on the basis of
the correction of the first air/fuel ratio control quantity
d) filtering the first air/fuel ratio signal to compensate for variations in the output
characteristics of the upstream sensor
4) assessing the efficiency of the catalytic converter by using e.g. the method of US5363647
(1 994) described above.

Other methods: see JP4181149 (1992), JP6129240 (1994)