Exhaust Gas Recirculation: Description and Operation

Fig. 19 Exhaust Gas Recirculation:

Fig. 21 Vacuum Modulator:

SYSTEM DESCRIPTION

The Exhaust Gas Recirculation system is used to dilute the incoming air/fuel mixture with recirculated exhaust gases. Dilution of the incoming mixture lowers the peak flame temperature limiting the formation of nitrous oxides (NOx).

EGR VALVE

The EGR valve 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 which in turn is controlled by the ECU.

VACUUM MODULATOR

The Vacuum Modulator Valve controls the amount of exhaust gases that are allowed into the intake manifold by sensing engine load conditions. The ECU controls the vacuum signal to the modulator which in turn controls the EGR valve.

VACUUM SWITCHING VALVE

The Vacuum Switching Valve (VSV) allow the ECU to control the EGR system. The vacuum signal used by the EGR system is controlled by the VSV in response to control signals from the ECU.