Engine Control Unit (Ecu) - Daewoo G424 Gasoline Service Manual

Engine Control Unit (ECU)

In order to obtain maximum emission reductions from
the exhaust gas catalyst, accurate control of the
engines operating air fuel ratio (AFR) is required. The
engine control unit (ECU) uses input from three
sources: excess oxygen information from the exhaust
gas oxygen sensor (EGO), ignition pulses (engine
RPM) and intake manifold pressure (high or low). This
input is used to apply a duty cycle and a rate of
change of that duty cycle to the fuel control valve
(FCV). The duty cycle of the FCV has a direct effect on
the AFR metered by the carburetor and burned by the
engine. ECU algorithms are calibrated for a balance of
optimal engine emissions, drive-ability, power and fuel
consumption.
Within the ECU closed-loop algorithms there are two
sets of calibration tables, one for high and one for low
manifold pressure. The proper table is selected based
on the input from the mechanical calibration of the
manifold pressure switch used. Each of the two tables
contains sixteen columns corresponding to sixteen
engine RPM operating ranges. The proper column is
selected based on engine rpm. These columns each
have eight calibrations that affect the rate of duty cycle
change and allow duty cycle stepping after EGO
voltage crosses the .5 V threshold. The duty cycle
stepping is used for AFR biasing and for rapid
recovery during transient operation. EGO voltage and
time since last EGO switch (across the .5 V threshold)
determine the column calibration to apply to the rate of
duty cycle change. There are additional calibrations
for FCV duty cycle at cold EGO startup and for the
number of ignition inputs per engine revolution.
During operation a normal sequence of events is as
follows:
If the EGO voltage is below .5 V, considered a lean
condition, the controller steps FCV duty cycle to a
lower value, then begins decreasing the FCV duty
G424 Service Manual
cycle at a constant rate. This decreases the flow of air
valve vacuum (AVV) through the FCV to the
secondary reference chamber of the fuel pressure
regulator (sometimes referred to as a vaporizer). This
vacuum is depleted at a relatively constant rate via a
vent orifice referenced to atmospheric pressure,
resulting in a pressure balance proportional to FCV
duty cycle and vent orifice size. The lower flow through
the FCV results in a higher overall chamber Pressure.
Which results in a higher fuel pressure to the
carburetor and a richer AFR. If the duty cycle
continues to lower longer than a calibrated number of
engine revolutions without an EGO switch, a different
calibration is selected resulting in higher rate of duty
cycle change until EGO switch.
The calibration tables determine the step size, rate of
duty cycle change and the number of engine
revolutions without an EGO before going to higher
rate.
If the EGO voltage is above .5 V, considered a rich
condition, the controller steps FCV duty cycle to a
higher value, then begins increasing the FCV duty
cycle at a constant rate. This increases the flow of AVV
through the FCV to the secondary reference chamber
of the fuel pressure regulator. The higher flow through
the FCV results in a lower overall chamber pressure,
which results in a lower fuel pressure to the carburetor
and a leaner AFR. If the duty cycle continues to lower
longer than a calibrated number of engine revolutions
without an EGO switch, a different calibration is
selected resulting in higher rate of duty cycle change
until EGO switch. The calibration tables determine the
step size, rate of duty cycle change and the number of
engine revolutions without an EGO before going to
higher rate.
93 LPG Fuel System(Low Emission Version)
6EV2149