Page 207 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

Mitsubishi Motors Corporation - Mitsubishi Electric Corporation 189

control unit and other components is supplied from an onboard battery via a key switch. An
alarm lamp driven upon detection of abnormality such as deterioration of the catalytic
converter and the like (indicated by a signal E) is connected to an output terminal of the
electronic control unit. Further, a vehicle speed sensor for detecting a speed of a motor vehicle
is installed in association with an axle. The operation of the fuel injector is controlled by the
electronic control unit in dependence on the running or operation state of the engine while
taking into account the air/hel ratio detected by the sensors 1 and 2.

The electronic control unit receives as the engine operation state indicating parameters or
quantities a variety of input signals including the throttle opening signal cp from the throttle
sensor, the pressure signal P from the pressure sensor indicating the pressure within the intake
manifold, the coolant water temperature signal T from the water temperature sensor, the idle
signal D from the idle switch, a vehicle speed signal S from a vehicle speed sensor, a rotation
or interrupt signal R generated upon every interruption of the electric conduction of the
ignition coil and serving as an interrupt signal and aidfuel ratio signals VI and VI supplied from
the first and second aidfuel ratio sensors I and 2, respectively. The electronic control unit
generates a fuel injection control signal J under the control through an air/fuel ratio feedback
control loop. The abnormality signal E for lighting the alarm lamp is generated upon detection
of occurrence of abnormality (such as deterioration of the catalytic converter) in the engine
operation.

The method of JP63231252 (1988) comprises the following steps:
1) feedback-controlling the engine aidfuel ratio according to the output signal of the upstream
oxygen sensor
2) detecting the output signals of the upstream and downstream sensors
3) detecting the difference of the maximum values of the respective output signals of the
upstream and downstream sensor
4) deciding that the catalytic converter must be replaced when this difference falls below a
predetermined value

The method of JP3031756 (1991) comprises the following steps:
1 ) feedback-controlling the engine aidfirel ratio according to the output signal of the upstream
oxygen sensor
2) calculating the width of the feedback correction factor
3) calculating the width of the change in the equivalent aidfirel ratio based on the air/hel ratio
measured by the downstream sensor
4) calculating the ratio of the width of the change in the equivalent aidhe1 ratio to the width of
the feedback correction factor
5) deciding that the catalytic converter has deteriorated when this ratio exceeds a
predetermined value.

The method of DE4233977 (1993) and US5417061 (1995) comprises the following steps: