Page 309 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Toyota Motor Co. Ltd. 29 I

I
High
measured
temp. T2

Low

LOW -

High
assumed temp. Ti

Fig. 13 1 (from EP0756071)

In the method of DE19701355 (1997), an electric heater is installed upstream of the catalytic
converter to heat the exhaust gas during light-off of the catalytic converter. When the engine
idles and certain engine predetermined deterioration operating conditions (except the activation
temperature of the converter) are satisfied, the electrical heater is supplied with electric current
to heat the catalytic converter to its activation temperature. When the duration of time that the
electrical heater needs to maintain the operation of the converter is longer than a
predetermined time duration then the catalytic converter is considered as deteriorated.

The methods of EP0770768 (1997) and EP0786586 (1997) comprise the following steps:
1) detecting the temperature of the exhaust gases downstream of the catalytic converter by
means of a temperature sensor
2) detecting the oxygen concentration of the exhaust gases upstream of the catalytic converter
by means of an oxygen sensor
3) calculating a degree of performance of the catalytic converter in a predetermined period
based on the detected temperature and oxygen concentration of the exhaust gases