Exhaust Gas Recirculation: Description and Operation

Differential Pressure Feedback EGR (DPFE) System:

The Exhaust Gas Recirculation (EGR) system is designed to:
- Reintroduce exhaust gas into the combustion cycle.
- Rower combustion temperatures.
- Reduce the formation of nitrous oxide.

The amount of exhaust gas reintroduced and the timing of the cycle varies by calibration. Timing and volume are controlled by:
- Engine rpm.
- Engine vacuum.
- Exhaust system back pressure.
- Engine coolant temperature.
- Throttle position.

The EGR system is a differential pressure feedback system, using a vacuum actuated EGR valve. Differential pressure feedback EGR is a subsonic closed loop EGR system. The differential pressure feedback EGR system:
- Monitors EGR flow rate by the pressure drop across the metering orifice.
- Uses an EGR backpressure transducer as the feedback device.
- Control pressure is varied by the valve movement using vacuum output of the EGR vacuum regulator solenoid.
- Uses the EGR valve only as a pressure regulator rather than a flow metering device.
- Allows for a more accurate assessment of EGR flow requirements.