Exhaust Gas Recirculation: Description and Operation

PURPOSE
The exhaust gas recirculation (EGR) system recirculates exhaust gasses into the air/fuel mixture to lower combustion temperature. Oxides of Nitrogen (NOx) emissions are reduced as a result of lower combustion chamber temperatures.

CONSTRUCTION
Precise metering of exhaust gas into the air/fuel mixture is necessary for maximum reduction of NOx while maintaining good engine performance. To achieve this control, the system uses the following components:
- Vacuum actuated EGR (control) valve
- EGR vacuum modulator assembly
- ECM controlled vacuum switching valve

OPERATION

EGR System Schematic View And Operating Conditions:

Refer to the following chart for component operation.

EGR System Components Operational Parameters:

The key to accurate exhaust gas metering is the backpressure controlled vacuum modulator assembly. Because backpressure increases proportionally with engine load the vacuum modulator can use this principle to precisely control the strength of the vacuum signal to the EGR valve.
In addition to the modulator assembly, a vacuum switching valve (VSV) is used to vent EGR valve signal vacuum during times when exhaust gas dilution of the intake charge would adversely affect engine performance.