-.-
25-6EMISSION CONTROL SYSTEMS- Exhaust Gas Recirculation (EGR) System
OPERATION
The engine control unit functions to calculate the
engine load, based upon the intake air volume
signals (from the air-flow sensor) and the rpm
signals (from the crank-angle sensor), and the
EGRcontrol solenoid valve is activated according to the
engine load. The
EGR amount is then regulated
according to the engine load calculated in this way.maintaining driveability during cold.
When, as a result of clogging of the
EGR cant’valve or as a result of an operational
malfunctio,.,the
EGR flow volume decreases, the EGR gas
temperature downstream. from the
EGR control
valve decreases. The engine control unit functions
to detect the
operation conditions of the EGRLoad
a Intake air volume/Engine rpmsystem by this characteristic.
If, however, the engine coolant temperature is low,
the actuation duty is attenuated, the
EGR control
valve activation negative pressure (vacuum) is
leaked from the throttle body A port, thus reducing
or interrupting the
EGR flow volume and therebyThe temperature of the
EGR gas is detected by the
EGR gas temperature sensor which is equipped at
the
EGR control valve; when the temperature
decreases to a low level, the engine warning light
(malfunction indicator light) illuminates in order to
advise the driver that a malfunction has occurred in
the
EGR system.
EGR
contcEGR control
solenoid valve
/Control
relay
1Engine control unit
Enginewarning
light
EMISSION CONTROL SYSTEMS - Exhaust Car Recirculation (EGR) System25-7Duty ratio
I .,
ON e-_-m-L--l
T2L1.TlOFF---
m
1c1-i1e2100260 msec. 60 msec.
EGR CONTROL VALVE
Spring
NOTEThe duty ratio is the ON duration ratio of 16.7 Hz pulse or
T2/T1.The higher the duty ratio, the more mean current flows to the
boost meter. and as a result, the boost meter reads the higher
value.The smaller is the duty ratio, the boost meter reads the smaller
value.
Diapl
.Valveiragm
To Intakemanifold
Exhaust gasApply vacuum
7EM0012
NOTEThis illustration indicates Non-Turbo models.7EMOO15The EGR control valve is a diaphragm that functions
to control the flow of
EGR gases by opening and
closing the valve according to the negative pressure
(vacuum) acting upon the partitioned chamber.When the negative pressure becomes stronger than
the spring force, the valve opens, as shown in the
illustration, and the exhaust gases can flow.
Valve
BlmetzII
17EMOO16
THERM0 VALVE
The therm0 valve functions in response to the temperature of
the engine coolant. thus controlling the negative pressure
acting upon the
EGR control valve.
The valve opens at a temperature of
65°C (149°F) or lower, and
closes at
65°C (149°F) or higher.
