Exhaust Gas Recirculation: Description and Operation

Exhaust Gas Recirculation Valve Solenoid




The EGR system is used to decrease emission levels of Oxides Of Nitrogen (NOx)which can have harmful environmental effects if released into the atmosphere in large quantities. NOx forms during combustion in amounts dependent on the concentration of oxygen in the combustion chamber and the temperature of the combustion process. By diluting the incoming fuel/air charge with exhaust gases, the peak combustion temperature is reduced due to the lower concentration of oxygen, and NOx emissions are also reduced.

The ECM has to determine an appropriate amount of exhaust gas to introduce into the combustion chamber. Too little EGR can yield high NOx, while too much can disrupt combustion events. The ECM considers ECT, TP, MAP,IAT,RPM, and VSS to determine an appropriate amount of EGR.

The EGR valve contains a position feedback circuit acting as a potentiometer which varies a signal voltage in the range of 0.5-5.4 V This allows for precise control of the actual position of the EGR pintle.

The solenoid is energized by current that creates an electromagnetic field. This field causes the armature assembly to pull upward, lifting the pintle a variable amount off the base. The exhaust gas then flows from the exhaust manifold port to the intake manifold. The position of the pintle is read by the pintle position sensor, and the ECM makes adjustments to the current to match the actual pintle position to a desired pintle position.

Too much EGR flow at idle, cruise, or cold operation can cause the following conditions:
^ Engine stops after cold start
^ Engine stops at idle after deceleration
^ Vehicle surges during cruise
^ Rough idle

Too little EGR flow allows combustion temperatures to get too high during acceleration and load conditions. This could cause:
^ Spark knock (detonation)
^ Engine overheating