Page 275 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Nissan Motor Co. 257

2) fixing the engine aidfuel ratio to a rich or a lean side for a fixed period
3) detecting a first exhaust gas temperature downstream of the catalytic converter
4) changing the engine air/hel ratio to a value opposite to this of step 2
5) detecting a second exhaust gas temperature downstream of the catalytic converter
6) calculating the difference between the measured first and second temperature values of
steps 3 and 5
7) comparing the calculated temperature difference with a predetermined value and drawing
conclusions about eficiency of the converter fiom this comparison

In JP7180536 (1995) one temperature sensor is mounted upstream of the catalytic converter
and one temperature sensor is installed inside or downstream of the catalytic converter. The
assessment of deterioration of the catalytic converter is based on the measured temperature
difference between the two sensors. A correction of the temperature difference takes place in
order to compensate a deterioration of the temperature sensors.

In JP7180537 (1995) a temperature sensor is mounted inside the catalytic converter in its
central part. The sensor has two sensing elements. One sensing element is positioned in the
center of a cross section of the converter and the other sensing element is positioned in a radial
position away from the center of the same cross section of the converter. The temperature
values measured by the two sensors are compared with each other. When a temperature
difference at a certain time point exceeds a predetermined threshold, it is decided that the
converter is deteriorated.

In the method of DE19643674 (1997) the temperature of the catalytic converter that is used
for the evaluation of the converter performance is determined indirectly from the operating
parameters of the engine. The method comprises the following steps:
1) determining if the engine starts-up from cold or warm conditions
2) determining a reference heat quantity in dependence on the condensation that takes place in
the converter during a cold start-up, or determining a reference heat quantity for the case of
a warm start-up, where no condensation takes place in the converter
3) evaluating the operating conditions of the engine
4) calculating the temperature of the catalytic converter in relation to the operating parameters
of the engine
5) evaluating the volume of the engine intake air
6) integrating in time (starting fiom engine start-up) the heat quantity that the exhaust gases
transfer to the converter during normal operating conditions of the engine. The heat
quantity is calculated from the temperature of the catalytic converter and the volume of
intake air
7) fixing a temperature value of the catalytic converter, when the total heat quantity
transferred to the catalytic converter from the exhaust gases of the engine is equal to or
smaller than the corresponding reference heat quantity