Page 306 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

288 Methods for Monitoring and Diagnosing the Efticiency of Catalytic Converters

Main converters are common type catalytic converters having metal or ceramic honeycomb
type substrates and having larger capacities than the heater-converters,. Since the main
converters are disposed downstream of the heater-converters, when the heater-converters
reach the activating temperature and the catalytic action starts in the heater-converters, the
exhaust gas which is heated by the oxidation of HC and CO components in the exhaust gas in
the heater-converters flows into the main converters. Thus the temperatures of the main
converters also reach the activating temperature in a short time after the engine starts.
The heaters are connected in parallel to an electric power source via lead wires. The electric
power source consists of a battery and an alternator of the engine. Also, a common relay is
provided on the lines. The relay is set ON and OFF by the signal from an electronic control
unit (ECU) in such a manner that ON and OFF of the heaters can be controlled simultaneously.
The ECU controls fuel injections and ignition timing of the engine and ON/OFF operation of
the heaters of the heater-converters.
To perform such controls, various signals, are fed to the input port of ECU via an A/D
converter. These signals are, for example, a voltage signal proportional to an amount of intake
air which is generated by an airflow meter (not shown) disposed on an intake air passage of the
engine, a voltage signal proportional to a temperature of the engine coolant which is generated
by a coolant temperature sensor (not shown) disposed on a water jacket of the engine and a
signal corresponding to a voltage of the battery. Also, a pulse signal from an engine speed
sensor (not shown) disposed on a distributor of the engine which represents an engine speed
and an ON/OFF signal of a starter motor (not shown) from starter switch (not shown) are fed
to the input port.
Further, temperature sensors are embedded in the catalyst beds of the heater-converters or are
installed upstream of the converters. Output signals of these temperature sensors are fed to
input port of the ECU via the A/D converter.
The output port of the ECU is connected to the relay via a driver circuit to control ON/OFF
operation of the heaters and of the heater-converters.

The method comprises the following steps:
1 ) electrically heating the EHC converters after the engine starts
2) detecting parameters relating to a temperature of each of the two EHC converters. The
parameters can be one of the following:
a) the measured temperatures of the catalyst beds of the converters
b) the rates of increase of the measured temperatures of the catalyst beds of the
converters
c) the differences between the temperatures of each catalyst bed and the
temperature of the stream of exhaust gases flowing into each of the converters
d) the electric currents flowing through the heating means of each of the EHC
converters
e) the electric voltages applied to the heating means of each of the EHC
converters
3) collating the values of the detected parameters of the two converters