Page 118 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

100 Methods for Monitoring and Diagnosing the Eficiency of Catalytic Converters

The method is also applicable in transient operation states of the engine (deceleration or
acceleration) and it is an improvement of the method of EP0547326 (1993).

The method of JW269330 (1995) uses the time delay difference in response of the upstream
and downstream sensors to judge the deterioration of the catalytic converter, This difference is
calculated from a time at which the output signal of the upstream sensor becomes lower than a
predetermined value to another time at which the output signal of the downstream sensor
becomes lower than the predetermined value. Half the maximum voltage output of the sensor
is used as a predetermined value.

The method of US5412941 (1995) prevents accuracy errors during determination of the
condition of a catalytic converter and comprises the steps of:
1) detecting an aidfuel ratio of the exhaust gas upstream of the catalytic converter
2) detecting the air/hel ratio of the exhaust gas downstream of the catalytic converter
3) controlling the aidfuel ratio of the engine by a feedback control based on the output of the
upstream aidfuel ratio sensor
4) determining whether the engine operating conditions are not appropriate to determine the
deterioration of the three-way catalyst, in which a period of a cycle of said feedback control
of the air/fuel ratio becomes larger than a value appropriate for the determination of the
deterioration of said three-way catalytic converter
5) prohibiting the determination of the deterioration of the three-way catalytic converter when
it is determined that the engine operating conditions are not appropriate
6) calculating lengths of the output signal response curves of said upstream and downstream
air/fuel ratio sensors
7) calculating areas surrounded by the output signal response curves and reference value lines
of said upstream and downstream air/fiel ratio sensors
8) calculating a ratio of said length of the output signal response curve of said upstream
aidfuel ratio sensor to said length of the output signal response curve of said downstream
aidfuel ratio sensor
9) calculating a ratio of said area of the output signal response curve of said upstream aidfuel
ratio sensor to said area of the output signal response curve of said downstream aidfuel
ratio sensor
10) determining whether said three-way catalytic converter has deteriorated in accordance with
said ratio of the lengths and said ratio of areas (see method of EP0547326 (1993)).

The condition determining step 4 comprises:
a) detecting the interval of reversals between a rich aidfie1 ratio side
and a lean air/hel ratio side of the output signal of the upstream
air/fuel ratio sensor, and determining that the engine operating
conditions are not appropriate for said determination of the
deterioration of the three-way catalyst when said interval of
reversals of the output of the upstream air/fiel ratio sensor becomes
longer than a predetermined value, or