Exhaust Gas Recirculation: Description and Operation

OPERATION-CAB/CHASSIS MODELS





The EGR (Exhaust Gas Recirculation) system is designed to reduce NOx in the exhaust system by reducing combustion temperatures. This is done by introducing inert gas (exhaust) into the combustion process. The intake air charge is diluted by a precisely metered amount of exhaust gas for the operating mode. For example at idle and part throttle, more EGR is introduced than at high-speed cruise conditions. A cooler (2) reduces the temperature of the exhaust gas before it is combined with the intake air, which increases the ability of the existing volume of inert gas to reduce NOx. The EGR cooler is cooled by the engine coolant.

The EGR system contains the following components:

- EGR Cooler (2)
- EGR Valve Assembly (5)
- EGR Valve Crossover Tube (4)
- EGR Temperature Sensor (7)
- EGR Valve Actuator (6)
- EGR Air Flow Control Valve (8)





EGR is active at low load and speed ranges. Control of EGR flow is based on engine load and engine speed. The ECM (Engine Control Module) gathers information from engine input sensors, and after evaluating the input signals, uses a stored performance map to operate the EGR Valve Actuator (2) and EGR Airflow Throttle Control Valve (3). The calculation allows for a precise EGR flow rate.

The EGR Valve Assembly (1) is located at the left front of the engine, in the upper corner of the intake manifold. The EGR valve has two poppet valves connected by a valve shaft. Cooled exhaust gases flow from the EGR cooler to the center of the valve. When the valves open, exhaust gasses flow into the intake air stream from both the top and the bottom of the passage.

The EGR valve motor (actuator) (2) is a three-phase, brushless DC motor controlled by the ECM. The motor assembly also contains three Hall-effect sensors that detect EGR valve position.