Exhaust Gas Recirculation: Description and Operation

Exhaust Gas Recirculation Wiring Diagram:

PURPOSE AND SYSTEM DESCRIPTION

The exhaust gas recirculation (EGR) system is used to reduce oxides of nitrogen (NOx) emissions. The atmosphere is made up of mostly Nitrogen, with a smaller percentage of oxygen, and a mixture of other gases. Oxygen and Nitrogen do not normally combine except at very high temperatures and pressures, conditions which are present in the combustion chamber especially during hard acceleration. When the engine is under load, the EGR valve admits a small amount of exhaust gas into the intake manifold to mix with the air/fuel charge. The exhaust gas is essentially inert (contains no fuel or oxidizer) and reduces peak combustion temperatures and pressures by absorbing some of the heat of combustion without participating in the actual burn. Greater amounts of exhaust gas are metered in as engine speed and load are increased.

The primary components of the EGR system are: the EGR valve; exhaust gas pipe; and ECM (Engine Control Module).

Digital EGR Valve:

COMPONENT DESCRIPTION - EGR VALVE CONSTRUCTION AND OPERATION

The digital EGR valve is designed to accurately supply exhaust gas to the engine, independent of manifold vacuum. The valve controls exhaust gas flow from the exhaust to the intake manifold through three calibrated orifices, each with a separate solenoid and pintle valve, to produce seven basic combinations of EGR flow. The ECM regulates EGR flow by varying solenoid "ON/OFF" signals. When a solenoid is energized, the armature, with attached shaft and swivel pintle, is lifted and the orifice is opened. The swivel pintle feature insures a good seal when the valve is closed, 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. Solenoids get battery voltage when the ignition is "ON" (through a common power terminal) and become energize when the ECM completes the circuit to ground. Each solenoid has its own ground circuit through the ECM, so they can be energized individually.


EGR CONTROL

To regulate EGR flow, the ECM controls the EGR solenoids depending on information from the following sensors:

^ Engine Coolant Temperature Sensor.
^ Throttle Position Sensor.
^ Manifold Absolute Pressure Sensor.


LOCATION:

The EGR valve is mounted on the right side of engine to manifold