Hyundai Sonata 1991 Shop Manual page 221

Y29FAOA
EXHAUST EMISSION CONTROL SYSTEM
EXHAUST EMISSION CONTROL SYSTEM
EXHAUST EMISSION CONTROL SYSTEM
Exhaust emissions (CO, HC, NOx) are controlled by a combination
of engine modifications and the addition of special control com-
ponents.
Modifications to the combustion chamber, intake manifold, cam-
shaft and ignition system form the basic control system. Addi-
tional control devices include a jet air system, an exhaust gas
recirculation (EGR) system and catalytic converters.
These systems have been integrated into a highly effective sys-
tem which controls exhaust emissions while maintaining good
driveability and fuel economy.
JET AIR SYSTEM
Y29FBOA
,
In addition to the intake valve and exhaust valve, a jet valve has
been provided for drawing jet air into the combustion chamber.
A jet air passage is provided in the throttle body, intake manifold
and cylinder head. Air flows through the two intake openings pro-
vided near the throttle valve of the throttle body, goes through
the passage in the intake manifold and cylinder head, and flows
through the jet valve and the jet opening into the combustion
chamber.
The jet valve is actuated by the same cam as the intake valve
and by a common rocker arm so that the jet valve and intake
valve open and close simultaneously.
The jet air flowing out of he jet valve scavenges the residual
gases around the spark plug and creates an ideal ignition
condition. It also produces a strong swirl in the combustion-
chamber which continues through out the compression stroke
and improves flame propagation after ignition, assuring high
combustion efficiency.
AIR/FUEL MIXTURE RATIO CONTROL SYSTEM
[Multi Point Injection (MPI) System]
V29FCOA
The MPI system is a system which employs the signals from the
oxygen sensor to activate and control the injector installed in the
manifold for each cylinder, thus precisely regulating the air/fuel
mixture ratio and reducing emissions.
This in turn allows the engine to produce exhaust gases of the
proper composition to permit the use of a three-way catalyst. The
three-way catalyst is designed to convert the three pollutants (1)
hydrocarbons (He), (2) carbon monoxide (CO), and (3) oxides of
nitrogen (NOx) into harmless substances. There are two
operating modes in the
MPI
system.
1. Open Loop-air fuel ratio is controlled by information pro-
grammed into the ECU at manufacture.
2. Closed Loop-air fuel ratio is varied by the ECU based on infor-
mation supplied by the oxygen sensor.
29-16
Intake valve
29Y035