Page 151 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Honda Motor Co. Ltd. 133

In JP4017758 (1992) the aidfuel ratio is switched to a rich state and the output signals of the
upstream and downstream sensors are detected and compared. The fuel supply is then cut off
for a certain time and the output signals of the two sensors are detected again. From the four in
total detected signals useful conclusions about the condition of the catalytic converter can be
drawn without any influence of the physical characteristics of the two sensors to be involved.

In the method of US5158059 (1992) an amount of residual fuel in the tank is compared with a
predetermined value and when the residual fuel is below a predetermined value, an abnormality
detection of the catalytic converter is inhibited. The detection method comprises the steps of
I) obtaining a first signal and a second signal based on respective signal outputs from the
upstream and downstream aidfuel ratio sensors when the fuel supply to the engine is
increased (high load)
2) obtaining a third signal and a fourth signal based on respective signals outputs from the
upstream and downstream aidfuel ratio sensors when the fuel supply to the engine is
interrupted (fuel cut)

vehicle speed

atm. pressure

electronic control unit

Fig. 62 (from US5381657)