The exhaust gas recirculation (EGR) system lowers the nitrogen oxide (NOx) emission level. When the air/fuel mixture combustion temperature is high, a large quantity of nitrogen oxides (NOx) is generated in the combustionchamber.
Therefore, this system recirculates part of emission gas from the exhaust port of the cylinder head to the combustion chamber through the intake manifold to decrease the air/fuel mixture combustion temperature, resulting in reductionof NOx.
The EGR flow rate is controlled by the EGR valve so as not to decrease the driveability.
When the engine coolant temperature is low, when the engine is at idle or when a wide open throttle operation is performed, the EGR valve is keptclosed, achieving no EGR.
In normal vehicle operation performed after warming up of the engine, the EGR valve is opened to carry out EGR.
In addition, the engine control module monitors the EGR system and illuminates the check engine/malfunction indicator lamp to let the driver know that thereis a malfunction.
Open Loop air/fuel ratio is controlled by information programmed into the ECM.
Closed Loop air/fuel ratio is adjusted by the ECM based on information supplied by the oxygen sensor.
