Exhaust Gas Recirculation: Description and Operation

Fig. 26 EGR system.:

Exhaust gas recirculation, Fig. 26 is used to reduce oxides of nitrogen emissions in the vehicle exhaust. EGR uses partial recirculation of the exhaust gases from a port in the cylinder head to a port in the intake manifold.

Fig. 30 Single type EGR control valve.:

The EGR valve, Fig. 30 controls the flow of exhaust gas in response to a vacuum control signal from a thermo valve and vacuum regulator valve. EGR flow is suspended during idle and full throttle operation.

Fig. 33 Vacuum regulator valve:

VACUUM REGULATOR VALVE (VRV)

The vacuum regulator valve, Fig. 33 is used to modify the EGR valve vacuum control signal at low engine load. The vacuum regulator valve reduces the EGR vacuum signal by bleeding air within the vacuum regulator valve when the pressure applied to the regulator valve is lower than the pre-set value corresponding to low engine loads. The pressure applied to the regulator valve is the sum of exhaust pressure and venturi vacuum.

The air bleed is closed when the pressure applied to the vacuum regulator valve is higher than the pre-set value corresponding to high engine load operation. The EGR valve then operates according to an unmodified vacuum signal.

Fig. 94 Thermo valve:

THERMO VALVE

The thermo valve, Fig. 94 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.