Exhaust Gas Recirculation: Description and Operation

EGR Valve:

PURPOSE
The Exhaust Gas Recirculation (EGR) system recirculates exhaust gas to the engine intake system to reduce combustion temperatures and exhaust gas Oxides of Nitrogen (NOx) content.

OPERATION
The amount of recirculation varies from zero with a cold engine, to a fixed flow rate with engine at operating temperature, intermediate load, and 1500 rpm minimum engine speed. The flow increases steadily as coolant temperature rises past 104°F (40°C). The system employs a control solenoid, triggered by the Electronic Control Assembly (ECA) and sensor system.

The ECA disables the EGR system under conditions of zero throttle opening, full throttle, low coolant temperature, low engine speed, transmission in neutral, or system malfunction by opening the EGR vent solenoid.

The EGR control solenoid and EGR vent solenoid are packaged together. The control solenoid functions to actuate the EGR system by allowing vacuum stored in the vacuum reservoir to reach the EGR valve. The vent solenoid relieves the vacuum at the EGR valve when the control solenoid closes.

A vacuum reservoir with integral check valve is used to collect vacuum during deceleration and store it for use during driving when the EGR must be used.