SECTION 19
SECTION 19
EXHAUST GAS
RE-CIRCULATION CONTROL
1.0 SPECIFICATION
Exhaust Gas Re-circulation Control
(EGR)
1.1 Introduction
The exhaust gas re-circulation system
provides a means to direct exhaust gases from the exhaust
manifold into the intake manifold. This is accomplished
using a vacuum diaphragm valve and an electronic vacuum
regulator valve (EVRV). Ported engine vacuum is directed
to the EVRV which processes a 128 Hz pulse width
modulated signal from the ECM to determine the amount of
regulated vacuum signal to be applied to the vacuum
diaphragm value (EGR is active with vacuum applied The
regulated vacuum signal is also electronically fed back
to the ECM for use in EGR diagnostics (see ?.1I Section
8).
2.0 Special Electronic Vacuum
Regulator Value (EVRV) Control Conditions
Under certain conditions, the E'IRV is
controlled independently of the EGR control algorithm.
These conditions involve high battery voltage engine not
running, diagnostic/factory test, I~U active and reset.
2.1 High Battery Voltage
The EGR duty cycle is set to 0% (EGR
off) if the battery voltage is greater than a nominal
16.9 volts for 200 msec.
2.2 Engine Not Running/Diagnostic
Mode
The EGR duty cycle set to 100% (EGR on)
if the engine is not running and the diagnostic mode is
selected. The EGR duty cycle is set 0% (EGR off) if the
engine is not running and diagnostic mode is not
selected.
2.3 Reset
The EGR duty cycle is set to 100% (EGR
on) when the ECM is reset.
2.4 Factory Test Mode
Duty cycle of the EGR output in factory
test mode is dependent on which test mode function is
enabled (see 3.2 Section 4). See the following chart:
Test Mode function EGR Duty Cycle
Mode 1 (All Off Mode) 0% (EGR off)
Mode 2 (I/O Check Mode) 50% @ 32 Hz. PWM rate
Mode 3 (Misc. Test Mode) 0% (EGR Off)
Mode 4 (I/O Check Mode) 50% @ 32 Hz. PWM rate
2.5 I2U
EGR duty cycle may be slewed if the HUD
and I2U are active and *KAFOPTI*, bit 0 is zero (=0).
3.0 Control Algorithm
Provided that the engine is running and
special control conditions are not present, the EVRV is
controlled by the EGR control algorithm. In accordance
with the control algorithm, the ECM will enable EGR when
coolant temperature, throttle position, and engine vacuum
criteria have been met. Conversely, if any of the above
criteria are not met, EGR is not enabled.
3.1 Enable/Disable Criteria
3.1.1 Coolant Temperature Criteria
The coolant temperature criteria for
EGR on is met when the coolant temperature equals or
exceeds *KEGRTEMI*. The coolant temperature criteria
shall always be met if *KEGRTEM1* is set equal to 0.
Setting *KEGRTEMI* equal to 255 will result in the
coolant temperature criteria never being met and EGR
never enabled.
3.1.2 Throttle Position Criteria
When the EGR is disabled, the throttle
position criteria for EGR on shall be met when throttle
position is greater than calibration memory parameter
*KF4TPSl*. When the EGR is enabled, it shall remain on if
the throttle position remains greater than calibration
memory parameter *KF4TPS2*. For proper system operation,
*KF4TPS1* must equal or exceed *KF4TPS2*. Setting
*KF4TPS1* and *KF4TPS2* equal to 255 will result in the
throttle position criteria never being met which disables
EGR
3.1.3. Engine Vacuum Criteria
When EGR is disabled, the engine vacuum
criteria for EGR on shall be met when engine vacuum is
less than or equal to the calibration memory parameter
*KEGRVAC2*. When EGR is enabled, it shall remain enabled
if engine vacuum remains less than or equal to the
calibration memory parameter *KEGRVAC1* for proper system
operation, *KEGRVAC1* must equal or exceed *KEGRAVAC2*.
Setting *KEGRVAC1* and *KEGRVAC2* to 255 will result in
the engine vacuum criteria always being met.
3.2 Tables
3.2.1 *F60* Table
The *F60* table provides the altitude
factor for adjusting BPW and EGR versus barometric
pressure and manifold air pressure.
The *F60* table is a two dimensional
lookup table with barometric pressure and manifold air
pressure as independent variables.
3.2.2 *F72* Table
The *F72* table provides the desired
percent EGR versus manifold vacuum and engine RPM.
The *F72* table is a three dimensional
lookup table with manifold vacuum and engine RPM as the
independent variables.
Manifold vacuum is defined as
Barometric pressure minus manifold absolute pressure.
3.2.3 *F73* Table
The *F73* table provides the EGR duty
cycle versus the EGR valve effective flow area.
The *F73* table is a two dimensional
lookup table with EGR valve effective flow area in units
of grams per second per kPa as the independent variable.
3.2.4 *F75* Table.
The *F75* table provides EGR flow
pressure. compensation versus pressure.
The *F75* table is a two dimensional
lookup table with barometric pressure in kPa as the
independent variable.
4.0 Computations
4.1 Engine Air Flow
The following computation shall be used
to obtain the airflow (1 bit = 0.25 grams/sec.) through
the engine:
Air Flow =
BPWM*KAIRF~w*2l8*KNUMcyL*25*AIRFUEL*NTRPMx32
Where: BPWM = Base pulse width for EGR
KAIRFLOW = Air Flow multiplier.
KNUNCYL = Number of cylinders*32.
AIR FUEL = Engine running air fuel
ratio*IO.
NTRPMX = Computed engine RPM scaled 25
RPM/bit.
4.2 Exhaust Back Pressure
The following computation shall be used
to obtain the exhaust system back pressure (kPa gage):
Rack Pressure =
KBP2*(AirFlow**2)+KBPI*AIRFL0W+KBP0
Where KBP0 = Back pressure multiplier
in KPA.
KBP1 = Back pressure multiplier in
KPA*sec/gram.
KBP2 = Back pressure multiplier in
KPA*sec*sec/gram*gram.
4.3 EGRFLOW
The following computation shall be used
to obtain the EGR value equivalent flow area for the
desired percent EGR
EGRFLOW = EGRDESA*AIRFLOW*F75(
BP+VAC)
256
Where EGRDESA = Desired Percent EGR
(altitude compensated).
AIRFLOW = Computed engine air flow.
F75 Table = EGR Flow pressure
compensation versus pressure.
4.4 EGR Solenoid Duty Cycle
The following computation shall be used
to obtain the EGR solenoid duty cycle:
EGR Duty Cycle = F73(EGRFLOW)
Where: F73 Table = EGR duty cycle
versus EGR valve Flow normalized to pressure across the
valve (grams/sec)/F75(KPA).
5.0 Computation Rate
The EGR logic is performed once per 100
msec.