EGR System Operation
The Exhaust Gas Recirculation (EGR) system is used to reduce NOx emissions by lowering combustion temperatures. Recycling metered amounts of exhaust gas back into the intake system lowers combustion temperatures. See Fig 1.
When engine is below operating temperature, no exhaust gas recirculation is obtained. Increase in engine temperature allows control valves to regulate vacuum to EGR valve for gas recirculation. Vacuum modulator is used to regulate exhaust backpressure and balance atmospheric pressure and vacuum, to allow EGR operation at heavy throttle.
Based on inputs from the coolant temperature sensor, engine RPM and throttle position sensor, the ECU helps control EGR operation. The ECU controls vacuum through a Vacuum Switching Valve (VSV).