Exhaust Gas Recirculation: Description and Operation

Digital EGR Valve:

PURPOSE
The digital EGR valve is designed to accurately supply exhaust gas to the engine (without the use of manifold vacuum) to reduce NOx (Oxides of Nitrogen) in exhaust emissions.

OPERATION
The digital EGR valve is opened by the ECM Quad Driver Module (QDM), grounding each respective solenoid circuit. The activated solenoid allows the pintle to raise, and exhaust gases flow into the intake manifold through three size-incremental orifices, to produce seven combinations. The exhaust gases then combine with the air/fuel mixture into the combustion chamber. If too much exhaust gas enters, combustion will not occur. Because of this, very little exhaust gas is allowed to pass through the valve, none at idle. The valve should only open when the engine is at operating temperature and above idle speed.

CONSTRUCTION:
The flow accuracy is dependent on the orifice size only, which results in improved control. The swivel pintle feature insures good sealing of the exhaust gas flow, reducing the need for critical assembly alignment. The effects of EGR leakage on idle quality are reduced because the shaft and seals are exposed to the exhaust pressure instead of manifold vacuum. The shafts are sealed from the exhaust chamber by floating seals held in place by the seal spring. These springs also hold the upper seals of the armature cavity in the solenoids. The solenoid coils are fastened together to maximize reliability and to seal the coils from the environment. The coils use a common power terminal with individual ground terminals.