Exhaust Gas Recirculation: Description and Operation

Exhaust Gas Recirculation System (EGR):

The EGR system reduces Oxides of Nitrogen (NOx) emissions. The atmosphere is made up of mostly Nitrogen, with a smaller percentage of oxygen, and a mixture of other gases. Oxygen and Nitrogen do not normally combine except at very high temperatures and pressures. These conditions are present in the combustion chamber, especially during hard acceleration. When the engine is under load, the EGR valve admits a small amount of exhaust gas into the intake manifold to mix with the air/fuel charge. The exhaust gas is essentially inert (contains no fuel or oxidizer) and reduces peak combustion temperatures and pressures by absorbing some of the heat of combustion without participating in the actual burn. Greater amounts of exhaust gas are metered in as engine speed and load increase.

EGR VALVE
The EGR control valve regulates the amount of exhaust gas flowing into the intake manifold, according to vacuum regulated by the duty solenoid valve.

EGR POSITION SENSOR
The EGR position sensor detects EGR control valve position and sends a signal to the ECU.

DUTY SOLENOID VALVE
The duty solenoid valve consists of a vacuum valve and a vent valve. The vacuum valve opens the vacuum passage to the EGR control valve, and the vent valve vents vacuum from the vacuum valve to control vacuum according to signals from the ECU.

ENGINE CONTROL UNIT (ECU)
The ECU senses the amount of EGR gas recirculated by the EGR position sensor signal and controls the opening duration of the vacuum and vent valves. The amount of exhaust gas recirculation is determined by the ignition coil signal, coolant temperature sensor, vacuum sensor, coolant temperature switch, and atmospheric pressure sensor.