Exhaust Gas Recirculation: Description and Operation
PURPOSEThis system is used to dilute the incoming air/fuel mixture with recirculated exhaust gases. Dilution of the incoming mixture lowers the peak flame temperature in the combustion chamber and thus, limits the formation of oxides of nitrogen (NOx).
OPERATION
The exhaust gas recirculation (EGR) System consists of a passage into the exhaust manifold and one into the intake manifold, two vacuum ports on the throttle body and three functional parts, described below.
EGR VALVE
This is a vacuum operated valve which opens and closes a passage from the exhaust manifold to the intake manifold. This allows flame temperature in the combustion chamber to be lowered by diluting the incoming mixture with exhaust gases. The EGR valve is controlled by the vacuum modulator and the vacuum switching valve.
VACUUM MODULATOR
This valve controls the amount of exhaust gases that are allowed into the intake manifold by sensing load conditions.
VACUUM SWITCHING VALVE
The VSV is controlled by the engine control module (ECM).
The following diagrams illustrate the interaction of the Vacuum Modulator and the Vacuum Switching Valve in controlling the operation of the EGR valve.
7A-FE EGR System Operation:
EGR System Operation:
