Exhaust Gas Recirculation: Description and Operation

Fig.145 - EGR System:

Description

The EGR System, Figs. 145, is designed to reduce oxides of nitrogen emission (NOx), by recirculating exhaust gas through the EGR valve and the intake manifold into the combustion chamber. It is composed of EGR valve, EGR control valve A and B, control switch, EGR control solenoid valves, thermosensor A, speed sensor and throttle opener solenoid valve. The EGR valve is operated by vacuum from the carburetor port and provides EGR volume proportional to engine loads (intake air volume) by the operation of the EGR control valve A & B.

The EGR system recirculates exhaust gas only after the engine is up to normal operating temperatures and then only while accelerating or cruising: these two conditions create the majority of NOx emission. EGR flow is cut off during idle, deceleration, and cold engine operation to assure good combustion during these conditions.

Operation

The vacuum signal is ported above the idle position of the throttle valve to eliminate EGR at idle.

In cold engine operation when the thermosensor A is on, the EGR control solenoid valve is energized and the EGR valve is closed for cut off.

When the engine coolant temperature exceeds the set temperature of the thermosensor A and ported vacuum is introduced through the EGR control solenoid valve A into the EGR valve and EGR control valve A. This opens the EGR valve allowing exhaust gas into the intake manifold.

EGR control valve B is normally closed. When manifold vacuum reaches the set level the valve opens allowing venturi vacuum to enter control valve A and the EGR valve.

When the intake manifold vacuum rises during deceleration, the control switch is turned on to activate the EGR CONTROL solenoid valve A and the EGR flow is cut off. The vacuum for the control switch is introduced through the throttle opener solenoid valve, which is operated by the speed sensor to prevent the control switch an EGR control solenoid valve A from chattering.

On all 1982 models, the speed sensor and vacuum switch are designed to control the EGR flow volume by activating the EGR control solenoid valve B" according to vehicle speed and engine load.