Page 274 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

256 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

as presented in the first embodiment of the invention, a first temperature sensor located at this
point can monitor the condition of the catalytic converter.
Since the temperature of the catalytic converter depends on the exhaust gas temperature it can
fluctuate. A more precise monitoring of the catalytic converter takes place then by locating a
second temperature sensor at point B, as presented in the second embodiment of the present
invention. The difference of the temperatures indicated by the two sensors gives then a more
reliable indication of the condition of the catalytic converter.

In the method of JP3050315 (1991) a first temperature sensor is installed upstream of the
catalytic converter and a second temperature sensor is installed inside the catalytic converter at
a point adjacent to the entrance of the catalytic converter. The difference of the two sensor
signals is formed and when this difference becomes lower than a reference value, a warning
signal is produced indicating a degraded catalytic converter.

The method of US5060474 (1991) comprises a system to detect failure of a catalytic
converter and a secondary air supply system installed upstream of the catalytic converter. The
part concerning the failure detection of the catalytic converter only is presented below. The
following steps are comprised:
1) controlling the secondary air supply to feed air in the exhaust system upstream of the
catalytic converter
2) deriving a first temperature of the exhaust system at a first position located between the
secondary air supply position and the catalytic converter, when secondary air is fed to the
exhaust system
3) deriving a second temperature of the exhaust gases at a second position located inside or
downstream of the catalytic converter, when secondary air is fed to the exhaust system
4) deriving a first difference between the first and second temperature
5) controlling the secondary air supply to stop feeding secondary air into the exhaust system
upstream of the catalytic converter
6) deriving a third temperature of the exhaust gases at said first position, when secondary air
supply is stopped
7) deriving a fourth temperature of the exhaust gases at said second position, when secondary
air supply is stopped
8) deriving a second difference between the third and fourth temperature
9) comparing the first difference with the second difference and when they are found equal
deciding that the catalytic converter is deteriorated when the first temperature is less than
the third temperature

In the method of JP6264724 (1994) an aidfitel regulation sensor is mounted in the exhaust
pipe upstream of the catalytic converter. A temperature sensor is mounted downstream of the
converter. The method comprises the following steps:
I) judging whether the engine operating condition of the engine is in a state to perform the
assessment of the efftciency of the catalytic converter