Exhaust gas recirculation – or EGR for short – significantly reduces nitrogen oxide (NOx) emissions. The EGR valve controls the exact quantity of exhaust gases that are fed back into the intake manifold. There, the exhaust gases displace part of the oxygen, therefore lowering the combustion temperature. This prevents the formation of some nitrogen oxides. This is particularly important for diesel engines.
There are two main types of EGR valves. One is vacuum controlled and uses an electro-pneumatic pressure transducer. The opening and closing thereof is operated by the engine control unit. The other is driven by a DC electric motor or stepper motor. Both electronic and vacuum variations are opened and closed subject to engine load.
The electro-pneumatic pressure transducer uses a vacuum that is taken from the intake manifold or generated by a vacuum pump. This is controlled by pulse width modulation to regulate the position of the pneumatic valve on the EGR valve; this regulates the amount of recirculated exhaust gas used by the engine.
Here, the position of the EGR valve is controlled by the electric EGR control valve. This results in a more accurate valve position, which is fed back to the engine control unit via a potentiometer.
Diesel engines use their EGR systems throughout their entire rev range, which can be up to 60% of the total intake at idle. This system also helps to raise cylinder temperature during the initial warm-up – this reduces noise significantly.
Consequences of a Defect
In diesel vehicles, the valves have large opening cross-sections due to the high recirculation rates. This can reduce the nitrogen oxide concentration by up to 50% and the formation of soot particles by approximately 10%. In gasoline engines, the cross-sections of the EGR valves are significantly smaller.
Due to the constant use and harsh operating conditions, EGR modules are widely used. A defective EGR valve not only results in a significant increase in nitrogen oxides in the exhaust gas, but can also have a negative effect on the other components, such as the diesel particulate filter. febi offers a wide range of high-quality EGR valves, most of which contain the required seals.