Page 210 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

192 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

The method of JP6264725 (1 995) comprises the following steps:
I) detecting the load of the engine and calculating a load accumulated value within a specific
time interval
2) checking whether or not the load accumulated value exceeds a fixed value and in case it
does
3) detecting deterioration of the catalytic converter based on the output signals of the
upstream and downstream oxygen sensors. The converter is considered as deteriorated
when the detected deterioration value calculated from the output signals of the oxygen
sensors is more than a fixed value.

The method of US5425234 (1995) comprises the following steps:
1) detecting concentration of a particular component of the exhaust gas upstream of the
catalytic converter to output an aidfirel ratio signal indicating said concentration
2) detecting concentration of the particular component of the exhaust gas downstream of the
catalytic converter to thereby output a downstream aidfirel ratio signal indicating the
concentration
3) determining a deterioration parameter value at every predetermined time interval on the
basis of the downstream aidfuel ratio signal
4) filtering the deterioration parameter value to output a filtered deterioration parameter value
5) determining deterioration of the catalytic converter when the filtered deterioration
parameter value exceeds a predetermined value for a predetermined period. The comparison
of the filtered deterioration parameter value with the predetermined value takes place when
I) a difference between a currently sampled value of the filtered deterioration
parameter value and a previously sampled value thereof exceeds a permissible upper
limit value and/or
11) a difference between a currently sampled value of the filtered deterioration
parameter value and a precedent sampled value thereof exceeds a permissible upper
limit value.

Fig. 86 refers to one embodiment of the invention. VOZ is the output signal of the downstream
sensor and VA,~ is the linear filtered output signal of the downstream sensor given by the
following expression

where:
(n) represents a current time point
(n-1) represents a precedent time point and
k, is a filtering coefficient (O<k,<l).