Electric EGR System (EEGR): Overview
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The EEGR system uses exhaust gas recirculation to control the oxides of nitrogen (NOx) emissions just like vacuum operated systems. The only difference is the way in which the exhaust gas is controlled.
The EEGR system consists of an electric motor/EGR valve integrated assembly, a PCM, and connecting wiring. Additionally a MAP sensor is also required. Operation of the system is as follows (Fig 1):
- Signals from the engine coolant temperature (ECT) or cylinder head temperature (CHT) sensor, throttle position (TP) sensor, mass air flow (MAF) sensor, crankshaft position (CKP) sensor and the manifold absolute pressure (MAP) sensor 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 will deactivate EEGR during idle, extended wide open throttle or whenever a failure is detected in an EEGR component or EGR required input.
- The PCM calculates the desired amount of EGR for a given set of engine operating conditions.
- The PCM in turn will output signals to the EEGR motor to move (advance or retract) a calibrated number of discrete steps. The electric stepper motor will directly actuate 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.
- A TMAP sensor is used to measure variations in manifold pressure as exhaust gas recirculation is introduced into the intake manifold. Variations in EGR being used will correlate to the TMAP signal (increasing EGR will increase manifold pressure values).