Exhaust Gas Recirculation: Description and Operation

EGR Components:

SYSTEM DESCRIPTION

The digital (EGR) valve is designed to accurately supply EGR to the engine without the use of intake manifold vacuum. The valve controls EGR flow from the exhaust to the intake manifold through two orifices of different sizes to produce three combinations of flow. 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.
The swivel pintel 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 ECM quad driver grounding each respective solenoid circuit. This 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. Tor this reason, veryy little exhaust gas is allowed to pass through the valve. The EGR valve is usually open under the following conditions:

^ Warm engine operation
^ Above idle speed
^ 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
2. Throttle Position Sensor(TPS)
3. Manifold Absolute Pressure(MAP)