Exhaust Gas Recirculation: Description and Operation

EGR System Operations Chart:

SYSTEM DESCRIPTION

The exhaust gas recirculation (EGR) system is used to dilute the incoming air/fuel mixture with recirculated exhaust gases. Dilution of the incoming mixture lowers the peak flame temperature thus limiting the formation of nitrous oxides (NOx). System components include the EGR valve, vacuum modulator, and vacuum switching valve (VSV). The vacuum modulator senses engine load and determines the amount of exhaust gas to recirculate. The electronic control unit (ECU) measures engine speed and temperature and decides when to open the VSV. The vacuum modulator then controls the EGR valve operation.

EGR System Operations:

EGR System Operations:

EGR VALVE

The vacuum operated EGR valve opens and closes a passage from the exhaust manifold to the intake manifold. Flame temperature in the combustion chamber is then lowered by diluting the incoming mixture with inert exhaust gases. The EGR valve is controlled directly by the vacuum modulator and indirectly by the ECU.

VACUUM MODULATOR


This valve controls the EGR valve and regulates the amount of recirculated exhaust gases that are allowed into the intake manifold by sensing engine load conditions.

VACUUM SWITCHING VALVE

The vacuum switching valve (VSV) bleeds vacuum from the EGR valve under specified conditions. The VSV is open when the ECU signals that coolant temperature is below 117°F or engine rpm exceeds 4,000. When coolant temperature is above 127°F and engine rpm is below 4,000, the ECU interupts voltage to the VSV and closes the valve. This allows the vacuum modulator to assume full control of the EGR valve operation.