Page 301 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Chapter 2.7

Toyota Motor Co. Ltd.

The method of EP0498598 (1992) is applied for the layout of fig. 127.
As illustrated in fig. 127, an engine capable of fuel combustion at lean air-fuel ratios (lean burn
engine) has an exhaust conduit where a lean NO, catalytic converter is installed. An exhaust
gas temperature control device is installed in a portion of the exhaust conduit upstream of the
lean NO, catalytic converter. When the exhaust gas temperature changes, a catalytic converter
temperature of the lean NO, catalytic converter changes according to the change in the exhaust
gas temperature. A portion of engine cooling water is led to the exhaust gas temperature
control device and the circulation amount of cooling water is controlled by a control valve so
that the exhaust gas temperature control device can control the exhaust gas temperature. The
engine cooling water-type exhaust gas temperature control device may be replaced by:
a) a device using introduction of secondary air
b) a device using an air-&el ratio control or
c) a device using an ignition timing control
For the case of diesel engines the exhaust gas temperature control device may be replaced by:
a) a device using a charging pressure control or
b) a device using an intake throttle valve control .
The operation of the exhaust gas temperature control device is controlled by an electronic
control unit (ECU).

In the portion of the exhaust conduit upstream of the lean NO, catalytic converter, a
hydrocarbon supply device (HC supply device) is provided. The HC supply device includes a
HC source, a HC supply port for introducing the HC (for NO, reducing purposes) from the
HC source into the portion of the exhaust conduit upstream of the lean NO, catalytic

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