Exhaust Gas Recirculation: Description and Operation

EGR System:

GENERAL DESCRIPTION
The Exhaust Gas Recirculation (EGR) system controls the formation of NOx (Oxides of Nitrogen) emissions by recirculating the exhaust gases into the combustion chamber. This is done through the intake manifold.


OPERATION
The Exhaust Gas Recirculation (EGR) system is controlled by the Engine Control Module (ECM) through an Exhaust Gas Recirculation vacuum regulator solenoid and pressure transducer. Vacuum is allowed to the EGR valve at acceleration and shut OFF upon deceleration or constant engine speed. The diaphragm mounted in the EGR modulator is operated by back pressure of the exhaust gas to open and close the valve. By this opening and closing action of the valve, the EGR modulator controls the vacuum transmitted to the EGR valve.

LOW LOAD CONDITION
Under a low load condition such as low speed driving, the exhaust pressure is low. In this state, the diaphragm in the EGR pressure transducer is pushed down by the spring force and the pressure transducer valve opens to allow the air into the vacuum passage from the outside. As a result, the vacuum transmitted to the EGR valve becomes smaller and so does the opening of the EGR valve. Thus, a lesser amount of exhaust gas is recirculated to the intake manifold.

HIGH LOAD CONDITION
Under a high load condition such as high speed driving the exhaust pressure is high. By the high exhaust pressure, the diaphragm in the pressure transducer is pushed up and closes the EGR valve. As the air does not enter the vacuum passage in this state, the vacuum transmitted to the EGR valve grows larger and so does the opening of the EGR valve. Thus, a larger amount of exhaust gas is recirculated to the intake manifold.

CONDITIONS FOR VACUUM FLOW
Under any of the following conditions, the ECM closes the vacuum passage of the EGR vacuum regulator solenoid. In this state, as the vacuum is not transmitted to the EGR valve, it remains closed:

^ The Engine Coolant Temperature (ECT) is low.
^ The throttle valve is at idle position.
^ The engine is running under high load.

Other than the above, EGR valve opens and closes in accordance with the EGR modulator operation.