Page 146 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

128 Methods for Monitoring and Diagnosing the Eficiency of Catalytic Converters

The target air/fbel ratio continues to vary at the greater amplitude and the longer period during
the preset continuation time TO. Immediately after the preset continuation time TO elapses, it is
determined whether or not the catalytic converter is saturated. When the catalytic converter is
not saturated, the dither amplitude AX and the dither period AT are hrther corrected and
increased. Therefore, as shown in fig. 60, the target aidfuel ratio varies at a fbrther greater
amplitude and a firther longer period. The target aidfuel ratio continues to vary at the further
greater amplitude and the further longer period during the next preset continuation time TO.

Immediately after the next preset continuation time TO elapses, it is determined whether or not
the catalytic converter is saturated. Such processes are reiterated until the saturation of the
catalytic converter is detected. It should be noted that variation of the target air/fbel ratio at a
greater amplitude and a longer period causes the catalytic converter to be more easily and
surely saturated. The detection of saturation of the catalytic converter is based on the fact that,
as shown in fig. 60, the difference AV2 between the maximum value Vh, and the minimum
value Vhin of the output voltage V2 of the downstream oxygen sensor is equal to or greater
than a predetermined reference value E when the catalytic converter is saturated.

When saturation of the catalytic converter is determined, the degree of deterioration of the
catalytic converter is determined in response to the current deterioration detection corrective
values p and y which are components of the current dither amplitude AA and the current dither
period AT. Low values of p, y to achieve saturation of the catalytic converter mean great
deterioration of the converter.

The degree of deterioration of the catalytic converter is detected each time the distance traveled
by the vehicle body increases by 2,000 km. The degree of deterioration of the catalytic
converter may be detected when the total time of travel of the vehicle body increases by each
preset time or when the total time of operation of the engine increases by each preset time.

Other methods of Nippon Denso Co.: see JP8338286 (1996)