Page 153 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Honda Motor Co. Ltd 135

In this way, any differences or variations between the two sensors are eliminated. If the
difference between the areas A, and A*' is smaller than a predetermined limit, the catalytic
converter is considered as degraded.

The method of US5191762 (1993) comprises the following steps:
1) starting to cut off the fuel supply to the engine when the engine is decelerated having the
throttle valve substantially filly closed (fig. 64)
2) resuming the fuel supply to the engine when the rotational speed of the engine has become
lower than a predetermined value. This resumption of &el supply comprises resuming
feedback control, in which the air/fuel ratio of a mixture supplied to the engine is controlled
to a predetermined value in response to a signal of the upstream sensor
3) measuring the time At which the output from the downstream air/fbel ratio sensor has
required to reach a predetermined reference value Vrer (fig. 64) after the resumption of the
fuel supply to the engine. This carrying out of time measurement takes place when I) the
temperature of the engine is higher than a predetermined value, or 11) after a predetermined
time period has elapsed after transition of the engine from starting mode to normal mode
4) determining that the three-way catalyst is deteriorated when said measured time At is
shorter than a predetermined time period (fig. 64).

v02 deteriorated
downstr.
sensor

Vref . . . - - -. - -
I
i
i

fuel __ time
cut cF feedback

Fig. 64 (from US5191762)