Page 103 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Toyota Motor Co. Ltd. 85

In the exhaust system, a three-way reducing and oxidizing catalytic converter is disposed in the
exhaust passage downstream of the exhaust manifold. The catalytic converter is able to remove
three pollutants in the exhaust gas, i.e., CO, HC and NO,, simultaneously.

An upstream oxygen sensor I is provided at the exhaust manifold , i.e., upstream of the
catalytic converter. A downstream oxygen sensor 2 is disposed at an exhaust pipe downstream
of the catalytic converter. The upstream oxygen sensor 1 and the downstream oxygen sensor 2
generate output signals corresponding to the concentration of the oxygen component in the
exhaust gas. More specifically, the oxygen sensors 1 and 2 generate output voltage signals
which are changed in accordance with whether the air-fuel ratio of the exhaust gas is rich or
lean, compared with the stoichiometric air-fuel ratio. The signals output by the oxygen sensors
1 and 2 are transmitted to the ND converter of the control circuit.

The control circuit, which consists of a microcomputer, may further comprise a central
processing unit (CPU), a read-only-memory (ROM) for storing a main routine and interrupt
routines such as a fuel injection routine, an ignition timing routine and constants, etc., a
random-access-memory (RAM) for storing temporary data, a backup RAM (B-RAM), and a
clock generator for generating various clock signals. The backup RAM is directly connected to
a battery (not shown), and therefore, the content of the backup RAM is preserved even when
the ignition switch (not shown) is turned off

A throttle valve operated by a vehicle driver, is provided in the intake air passage, together
with an idle switch for detecting the opening of the throttle valve and generating a signal when
the throttle valve is fully closed. This signal is supplied to the I/O interface of the control
circuit.

A secondary air supply valve for introducing secondary air to the exhaust manifold is provided
to thereby reduce the emission of HC and CO during a deceleration or idling operation of the
engine.
An alarm which is activated when it is determined that the catalytic converter has deteriorated.

A down counter, a flip-flop , and a drive circuit are provided in the control circuit for
controlling the fuel injection valve.

When a he1 injection amount is calculated, the fuel injection amount is preset in the down
counter, and simultaneously, the flip-flop is set, and as a result, the drive circuit initiates the
activation of the fuel injection valve. On the other hand, the down counter counts up the clock
signal from the clock generator, and finally, a logic "1" signal is generated from the terminal of
the down counter, to reset the flip-flop, so that the drive circuit stops the activation of the fuel
injection valve, whereby an amount of fuel corresponding to the fuel injection amount TAU is
supplied to the cylinders.