Page 185 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Mazda Motor Corporation 167

Fig. 75 (from US5233829)

The method comprises the following steps:
1) detecting an emission level of exhaust gas upstream of each secondary catalytic converter
by means of the first exhaust sensors installed upstream of the secondary catalytic
converters.
2) detecting an emission level of exhaust gas downstream of each secondary catalytic
converter by means of the second sensors installed downstream of the secondary catalytic
converters.
3) detecting an emission level of exhaust gas downstream of the main catalytic converter by
means of the third sensor installed downstream of the main catalytic converter.
4) feedback controlling aidtiel ratios for said two groups of cylinders independently based on
emission levels detected by each first aidfuel sensor
5) detecting vehicle operating conditions (specific throttle opening and specific engine speed)
6) feedback-controlling an air/tiel ratio for said two groups of cylinders based on an emission
level detected by the second emission sensor only when detecting a specific vehicle
operating condition