Page 150 - Methods For Monitoring And Diagnosing The Efficiency Of Catalytic Converters A Patent - oriented Survey

132 Methods for Monitoring and Diagnosing the Eficiency of Catalytic Converters

throttle valve for supplying an electric signal indicative of the sensed absolute pressure within
the intake pipe to the ECU. An intake air temperature sensor is inserted into the intake pipe at
a location downstream of the intake pipe absolute pressure sensor for supplying an electric
signal indicative of the sensed intake air temperature to the ECU.

An engine coolant temperature sensor, which may be formed of a thermistor or the like, is
mounted in the cylinder block of the engine, for supplying an electric signal indicative of the
sensed engine coolant temperature to the ECU. An engine rotational speed sensor and a
cylinder-discriminating sensor are arranged in facing relation to a camshaft or a crankshaft of
the engine, neither of which is shown. The engine rotational speed sensor generates a pulse as
a TDC (top dead center) signal pulse at each of predetermined crank angles whenever the
crankshaft rotates through 180 degrees, while the cylinder-discriminating sensor generates a
pulse at a predetermined crank angle of a particular cylinder of the engine, both of the pulses
being supplied to the ECU

A three-way catalyst is arranged within an exhaust pipe connected to the cylinder block of the
engine for puritjring noxious components such as HC, CO, and NO,. Oxygen sensors as air-
fuel ratio sensors are mounted in the exhaust pipe at locations upstream and downstream of the
three-way catalyst, respectively, for sensing the concentration of oxygen present in exhaust
gases emitted from the engine and supplying electric signals in accordance with the output
values VI, Vz thereof to the ECU. Further, a catalyst temperature sensor is mounted on the
three-way catalyst for detecting the temperature of same and supplying a signal indicative of
the detected catalyst temperature to the ECU.

A vehicle speed sensor is connected to the ECU for detecting the vehicle speed V and
supplying a signal indicative of the detected vehicle speed V to the ECU. Further connected to
the ECU is an LED (light emitting diode) for raising an alarm when deterioration of the three-
way catalyst has been detected by the present method in a manner described in detail herein
below.

The ECU comprises an input circuit having the functions of shaping the wave forms of input
signals from various sensors, shifting the voltage levels of sensor output signals to a
predetermined level, converting analog signals from analog-output sensors to digital signals,
and so forth, a central processing unit (hereinafter called "the CPU"), memory means storing
various operational programs which are executed in the CPU and for storing results of
calculations therefiom, etc., and an output circuit which outputs driving signals to the fbel
injection valves and the LED.
The CPU operates in response to the above mentioned signals from the sensors to determine
operating conditions in which the engine is operating, such as an air-fuel ratio feedback control
region in which the fuel supply is controlled in response to the detected oxygen concentration
in the exhaust gases, and open-loop control regions including a region in which fbel supply
should be increased under a high load condition of the engine, and a fbel cut region, and
calculates, based upon the determined operating conditions, the valve opening period or fuel
injection period over which the fuel injection valves are to be opened in synchronism with
inputting of TDC signal pulses to the ECU.