Page 125 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Toyota Motor Co. Ltd. 107

The method of EP0770767 (1 997) comprises the following steps:
I) detecting the aidhel concentration of the exhaust gases upstream of the three-way catalytic
converter by means of an upstream aidfie1 sensor
2) detecting the oxygen concentration of the exhaust gases downstream of the three-way
catalytic converter by means of a downstream oxygen sensor
3) feedback-controlling the engine air/fGel ratio based on the output signal of the upstream
sensor. The feedback correction amount consists of
a) a proportional term to achieve the stoichiometric air/hel ratio and
b) an integral term for bringing an integrated value of an error between
the actual air/fiel ratio and the stoichiometric aidfie1 ratio to zero
4) determining deterioration of the three-way catalytic converter on the basis of
a) the length of a response curve that the output of the downstream
sensor describes during the time that the aidfie1 ratio is feedback-
controlled, or
b) the ratio of the response curve of the output signal of the
downstream sensor with a deterioration determination reference
value during the time that the air/fiel ratio is feedback-controlled.

DETECT I ON
INTERRUPTED

Fig. 53 (from EP0770767)

The method hrther comprises the steps.