Exhaust Gas Recirculation: Description and Operation

EGR Valve Control Schematic:

Exhaust Gas Recirculation (EGR) Flow:

EGR System Components:

EXHAUST FLOW
Exhaust gases are routed to the engine through a corrugated semiflexible feed pipe (EGR valve pipe) which connects the crossover exhaust pipe to the crossover water pump housing.

In the crossover water pump housing, exhaust gases are precisely metered by the PCM controlled EGR Valve, then cooled by engine coolant and finally routed to the front and rear cylinder heads. A potential drawback with EGR is that for certain driving schedules, deposits can accumulate when hot exhaust gases are cooled. The Northstar system uses the crossover water pump housing as a cross-flow heat exchanger to cool exhaust gases in large easily cleaned passages to virtually eliminate any concern with deposit accumulation during the service life of the engine. This is done by having the cooling passage reduce EGR gasses below their deposit forming temperature prior to routing these gasses into cylinder distribution channels.

In each cylinder bank, exhaust gases travel under the intake manifold along an irregularly shaped sandwich passage made up of the aluminum alloy cylinder head and a non-metallic distribution plate. Engine vacuum acts to draw exhaust gases through outlets in the distribution plate where mixing with the incoming fuel/air charges for each cylinder occurs. Although the openings look small, the EGR valve pintle is the flow limiter in this system.

The PCM monitors the following sensors to control the linear EGR valve:
- Coolant Temperature (CT) Sensor
- Throttle Position (TP) Sensor
- Manifold Pressure (MAP)
- Manifold Air Temperature (MAT)
- Throttle Switch (ISC)
- RPM data
- Vehicle Speed Sensor (VSS)

CIRCUIT OPERATION
- Output messages are then sent to the EGR system indicating the proper amount of exhaust gas recirculation necessary to lower combustion temperatures.

- The solenoid assembly is energized by 12 volt current which enters the valve through an electrical connector, then flows through the solenoid assembly to the PCM and creates an electromagnetic field.

- This field causes the armature assembly to be pulled upward, lifting the pintle a variable amount off the base.

- The exhaust gas then flows from the exhaust manifold (through the orifice) to the cylinder distribution channels.

- The height of the pintle is read by the pintle position sensor, and the PCM closes the loop on desired position versus actual position read, changing the pulse width modulated command to the solenoid accordingly, until the actual pintle position equals the desired pintle position. This results in improved accuracy.