Page 225 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Chapter 1.14

General Motors Corp.

Fig. 92 shows a typical engine layout used by General Motors Corp. for controlling an internal
combustion engine and for detecting the deterioration of a catalytic converter.
An air metering means, such as a conventional butterfly valve (throttle) is provided in the inlet
air path above which is located an airflow meter for measuring mass airflow into the engine
and providing an output signal MAF indicative thereof. Air passing through the inlet air path
enters an engine intake manifold (not shown) in which is disposed an air pressure sensor for
measuring the absolute pressure of air in proximity thereto, and providing an output signal
MAP indicative thereof.

A coolant temperature sensor is located in an engine coolant circulation path (not shown) to
measure the temperature of the coolant passing by the sensor and to output a signal TEMP
indicative thereof. The crankshaft rotates through operation of the engine at a rotational rate
proportional to engine speed and a crank-angle sensor measures the engine speed.

The inlet air is combined with inlet fuel and the aidfuel mixture combusted in the engine
through engine operation, and a substantial portion of the combustion products are drawn out
of the engine via the exhaust pipe to a catalytic converter. An upstream oxygen sensor 1 is
disposed in the exhaust gas pipe in position to sense the oxygen content of the engine exhaust
gas before treatment thereof by the converter, and to output a signal PREXAT indicative
thereof A downstream oxygen sensor 2 is located in the exhaust pipe in position to sense the
oxygen content of the engine exhaust gas after treatment thereof by the converter, and to
output a signal POSTCAT indicative thereof.

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