Exhaust Gas Recirculation: Description and Operation

Digital EGR Valve:

SYSTEM DESCRIPTION

The digital EGR valve is designed to accurately supply exhaust gas to the engine without the use of manifold vacuum. The valve controls exhaust gas flow from the exhaust to the intake manifold through two orifices, to produce three combinations. When the solenoid is energized, the armature, with attached shaft and swivel pintle, is lifted and the orifice is opened.
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.
The digital EGR valve is opened by the ECM Quad Driver Module (QDM), grounding each respective solenoid circuit. This activates the solenoid, allowing the pintle to raise, and exhaust gases to flow into the intake manifold. 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, above idle speed and a vehicle speed present.

EGR CONTROL

To regulate EGR flow, the ECM controls the EGR solenoids. The ECM uses the information from the the following sensors to control the flow:

1. Coolant temperature (CTS).
2. Throttle Position Sensor (TPS).
3. Mass Air Flow (MAF) or Manifold Absolute Pressure (MAP).
4. Vehicle speed sensor.