Exhaust Gas Recirculation: Description and Operation

EXHAUST GAS RECIRCULATION (EGR) SYSTEM

Overview
The EGR system controls oxides of nitrogen (NOx) emissions. Small amounts of exhaust gases are recirculated back into the combustion chamber to mix with the air/fuel charge. The combustion chamber temperature is thereby reduced, lowering NOx emissions.

Electric EGR (EEGR) System

Overview
The EEGR system consists of an electric motor/EGR valve integrated assembly, the powertrain control module (PCM), and the connecting wiring. Additionally a manifold absolute pressure (MAP) sensor is also required. Operation of the system is as follows:
1. The EEGR system receives signals from the cylinder head temperature (CHT), throttle position (TP), mass air flow (MAF), crankshaft position (CKP) sensor and the MAP sensors to provide information on engine operating conditions to the PCM. The engine must be warm, stable, and running at a moderate load and RPM before the EEGR system is activated. The PCM deactivates the EEGR during idle, extended wide open throttle (WOT), or whenever a concern is detected in an EEGR component or an EGR required input.
2. The PCM calculates the desired amount of EGR for a given set of engine operating conditions.
3. The PCM outputs signals to the EEGR motor to move (advance or retract) a calibrated number of discrete steps. The electric stepper motor directly actuates the EEGR valve independent of engine vacuum. The EEGR valve is commanded from 0 to 52 discrete steps to get the EGR valve from a fully closed to fully open position. The position of the EGR valve determines the EGR flow.
4. A MAP sensor is used to measure variations in manifold pressure as exhaust gas recirculation is introduced into the intake manifold. Variations in EGR being used correlate to the MAP signal (increasing EGR increases manifold pressure values).

Electric EGR System:

Hardware
The EEGR valve is a water-cooled motor/valve assembly. The motor is commanded to move in 52 discrete steps as it acts directly on the EEGR valve. The position of the valve determines the rate of EGR. The built-in spring works to close the valve against the motor opening force.

Electric EGR Motor/Valve Assembly: