Exhaust Gas Recirculation: Description and Operation

Fig. 25 EGR system.:

Exhaust gas recirculation, Fig. 25 is used to reduce oxides of nitrogen emissions in the vehicle exhaust.

Fig. 30 Single type EGR control valve.:

EGR uses partial recirculation of the exhaust gases from a port in the cylinder head to a port in the intake manifold. The EGR valve, Fig. 30 controls the flow of exhaust gas in response to a vacuum control signal from a thermo valve.

Fig. 33 Sub-EGR control valve:

Final control of EGR flow is determined by the sub-EGR valve, Fig. 33. At idle the sub-EGR valve closes preventing drivability problems associated with EGR operation at idle.

Fig. 111 Thermo valve:

THERMO VALVE

The thermo valve, Fig. 111 in the EGR vacuum supply line is a vacuum switch sensitive to engine coolant temperature. The thermo valve eliminates the vacuum signal to the EGR valve during warm-up when fewer NOx emissions are generated. Less EGR flow during warm-up helps to maintain acceptable driveability.