Exhaust Gas Recirculation: Description and Operation

Fig. 4 Feedback Carburetor Control System (Federal):

EGR OPERATION

Exhaust gas recirculation is used to reduce oxides of nitrogen emissions in the vehicle exhaust. EGR uses partial recirculation of exhaust gases from a port in the cylinder head to a port in the intake manifold. The EGR valve controls the flow of exhaust gas in response to ported vacuum

Fig. 48 Thermovalve:

THERMO VALVE

A thermo valve is used to prevent EGR operation until the engine has reached operating temperature. This improves driveability while the engine is cold. NOx emissions are minimal during engine warm-up anyway due to the relatively low combustion temperatures reached in a cold engine.

Fig. 50 Vacuum Regulator Valve:

VACUUM REGULATOR VALVE (VRV)

The VRV is used to modify the port vacuum signal that controls the EGR valve. At low engine load the VRV reduces the vacuum signal to the EGR valve.

Fig. 51 Operation Of The Vacuum Regulator Valve (Idle Or W.O.T.):

VACUUM REGULATOR VALVE OPERATION

During idle or wide open throttle operation ported vacuum is low and the EGR valve is closed by spring force to ensure stable idle operation.

Fig. 52 Operation Of The Vacuum Regulator Valve (Coolant Is Cold):

When the engine is cold the thermo valve vents ported vacuum to atmosphere and prevents EGR valve operation.

Fig. 53 Operation Of The Vacuum Regulator Valve (Light To Mod. Eng. Load):

During light to moderate engine load operation ported vacuum increases and opens the EGR valve. Exhaust gas flow through the EGR venturi creates a vacuum which is applied to the lower chamber of the VRV.

Fig. 54 Operation Of Vacuum Regulator Valve (Venturi Pres. Regulates EGR Flow):

The increasing vacuum applied to the lower chamber of the VRV causes the poppet valve inside the VRV to open and vent ported vacuum to atmosphere. The loss of vacuum causes the EGR valve to begin to close. The reduced flow through the venturi reduces the vacuum applied to the VRV and causes the poppet valve to move toward the closed position. The resulting closed loop control of the EGR valve improves driveablity while maintaining a low NOx emissions output.

Fig. 55 Operation Of The Vacuum Regulator Valve (Heavy Engine Load):

During heavy engine load operation ported vacuum acts on the middle chamber of the VRV closing the poppet valve and preventing the escape of port vacuum. The EGR responds directly to the port vacuum signal increasing EGR flow rate to minimize NOx emissions.