Page 292 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

274 Methods for Monitoring and Diagnosing the Eficiency of Catalytic Converters

positioned before the intake manifold of the engine to detect the mass flow rate of air entering
the intake manifold. The MAF sensor preferably takes the form of a hot wire anemometer
which transmits a MAF signal. which is indicative of the mass flow rate of air entering the
intake manifold, to the EEC. A Heated Exhaust Gas Oxygen (HEGO) sensor positioned
upstream of the catalytic converter on the first pipe detects the equilibrium concentration of
oxygen in the exhaust gas generated by the engine and transmits a representative HEGO signal
to the EEC. A Malfunction Indicator Light (MIL) which is preferably positioned in the
passenger compartment of the vehicle, on the instrument panel, provides, in response to a
malfunction signal, an indication to a driver of the vehicle of a malfunction as determined by
the EEC. The EEC performs a variety of engine control and diagnostic hnctions including
control of fuel injection and spark timing via a plurality of signals.

The EEC preferably includes a central processing unit, a read-only memory (ROM) for storing
control programs, a random-access memory (RAM) for temporary data storage, a keep-alive-
memory (KAM) for storing learned values, and a conventional data bus and I/O ports for
transmitting and receiving signals to and from the engine.

A temperature sensor module connects to a plurality of temperature sensors, which sense the
temperature at spaced intervals of a catalyst material in the catalytic converter. Each of the
temperature sensors generates a signal which is indicative of the temperature in the catalyst
material at the location of the temperature sensor and transmits a representative signal to the
temperature sensor module which time multiplexes the signals received From each of the
temperature sensors and transmits a multiplexed temperature signal to the EEC. A
temperature sensor is additionally installed upstream of the catalytic converter to measure the
temperature of the exhaust gases entering the catalytic converter.

The determination of the HC conversion-efficiency of the converter is carried out as follows:
1) checking at least a first operating parameter to determine if the engine is operating within a
predetermined operating range (e.g. engine operating temperature). If the condition is
satisfied then
2) measuring the temperature of the exhaust gas entering the catalytic converter
3) measuring the temperature of the catalyst substrate in the catalytic converter at the plurality
of cross sections for a predetermined number of time intervals
4) generating as a function of the measured temperature of the exhaust gas entering the
catalytic converter and the measured temperature of the catalyst substrate, an energy value
indicative of the total energy generated in the converter over the predetermined number of
time intervals (thermal power model)
5) comparing the generated total energy value to a predetermined total energy value
6) providing an indication of the HC conversion-efficiency of the catalytic converter if the total
energy value deviates from the predetermined energy value by more than a predetermined
deviation amount