Page 184 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

166 Methods for Monitoring and Diagnosing the Efficiency of Catalytic Converters

converters is smaller in capacity than the main catalytic converter in order to be activated very
fast after start up of the engine.
Upstream from the secondary catalytic converters, first exhaust sensors are disposed.
Downstream from the secondary catalytic converters, second exhaust sensors are provided.
Downstream from the main catalytic converter, a third exhaust sensor is provided. These
exhaust sensors detect the emission level of residual oxygen in exhaust gases.
Air/fuel ratio feedback control is performed by a electric control unit (ECU) incorporated in
the engine. The electric control unit also determines fimctional deterioration of the catalytic
converters. It receives various signals, such as an air flow rate signal from the air flow sensor
representative of an air flow rate, a throttle opening signal from the throttle opening sensor
representative a throttle opening of the throttle valve, a vehicle speed signal from a speed
sensor representative of a vehicle speed, an engine speed signal from an engine speed sensor
representative of an engine speed in rpm, a temperature signal from a temperature sensor
representative of the temperature of engine coolant, and emission level signals from all exhaust
sensors representative, respectively, of emission levels of residual oxygen in exhaust gas. The
air/f%el ratio control and the deterioration detection or determination are executed based on
these signals.
In addition, the electronic control unit controls a warning lamp to signal critical deterioration
of the secondary catalytic converters, as well as critical deterioration of the main catalytic
converter.
Airifbe1 ratio control is accomplished as the electronic control unit reads each signal. The
electronic control unit calculates the amount of air to be supplied into the combustion chamber
for each cycle based on an air flow rate signal and an engine speed signal. Subsequently, the
electronic control unit calculates, based on the calculated amount of air, a basic fuel injection
rate at which the fuel injection valve injects he1 into the combustion chamber. Thereafter, the
electronic control unit decides whether or not the engine is put in engine operating conditions
for the air/fbel ratio feedback control. That is, the aidfuel feedback condition is fulfilled when
the engine operates in a specific engine operating range defined by throttle opening, which
represents engine load, and engine speed, and in a specific range of cooling water temperatures
higher than a predetermined temperature. If in fact the engine operates in both the specific
ranges, the electronic control unit controls the fuel injection valves so that the optimal aidfuel
ratio is achieved for each row of the cylinders of the left and right cylinder banks.

Aidfuel feedback control is executed e.g. for the left cylinder bank in such a manner that the
electronic control unit sets a feedback correction value for an increase in fbel injection rate
when an emission level signal from the first exhaust sensor indicates a leaner air/kel ratio. The
electronic control unit also sets the feedback correction value for a decrease in fuel injection
rate when an emission level signal from the first exhaust sensor indicates a richer air/fkel ratio.
An actual fuel injection rate is determined after a correction of the basic fuel injection rate by
the feedback correction value and the temperature of cooling water. The electronic control unit
provides an injection signal corresponding to the actual fuel injection rate to the fuel injection
valves for the row of the cylinders in the left cylinder bank.