EGR Valve: Description and Operation

Digital EGR Valve:

Digital EGR Solenoid Wiring Schematic:

PURPOSE
The digital Exhaust Gas Recirculation (EGR) valve is designed to accurately supply EGR to an engine, independent of intake manifold vacuum. The valve controls EGR flow from the exhaust to the intake manifold through three orifices which increment in size to produce seven combinations. When a solenoid is energized, the armature, with attached shaft and swivel pintle is lifted, opening the orifice. The flow accuracy is dependent on metering orifice size only, which results in improved control.

OPERATION
The swivel pintle feature insures good sealing of exhaust gas, reducing the need of critical assembly alignment. In addition, the effects of EGR leakage on idle quality are reduced because the shaft and seals are exposed to 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 that seal 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.

The digital EGR valve is opened by the Powertrain Control Module (PCM) Quad-Driver (QDR), grounding each respective solenoid circuit. This quad-driver activates the solenoid, raises the pintle, and allows exhaust gas flow into the intake manifold. The exhaust gas then moves with the air/fuel mixture into the combustion chamber. If too much exhaust gas enters, combustion will not occur. For this reason, very little exhaust gas is allowed to pass through the valve, with virtually none at idle. The EGR valve is usually open under the following conditions:

^ Warm engine operation.
^ Above idle speed.