What is an EGR valve? Structure and function in the car

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  • Post last modified:August 8, 2022
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With the function of reducing the combustion temperature in the combustion chamber, EGR ensures that the emission of nitrogen oxides into the environment. In the following article, we will explain what is an EGR valve and what does an EGR valve do?

EGR valve

What is an EGR valve?

The EGR valve stand for exhaust gas recirculation valve. It is part of the exhaust system in the car. Whether BMW, Opel, Mercedes-Benz or VW, the exhaust gas recirculation valve is installed in the immediate vicinity of the engine block, directly at the base of the exhaust manifold. The EGR valve is often also referred to as the EGR valve.

However, there is no difference between these two terms. EGR is simply the abbreviation of the English name: Exhaust Gas Recirculation. In the following part, learn more about your car and the valve used for exhaust gas recirculation.

What does an EGR valve do?

The EGR valve controls exhaust gas recirculation and thus the reduction of dangerous nitrogen oxides that are produced during the combustion of diesel fuel. In addition, the engine is fed back its own exhaust gases. This lowers the combustion temperature, and fewer nitrogen oxides are released.

Gasoline engines also benefit from an EGR module. The exhaust gases supplied to the combustion air cause the throttle valve to open further. This, in turn, reduces fuel losses caused by throttling and saves gasoline.

How does an EGR valve work?

How does an EGR valve work

When the engine is running, the exhaust gases are first discharged via the exhaust manifold. Next, some of these exhaust gases enter the exhaust gas recirculation valve or valve chamber via the side or center flange. From there, the exhaust gases flow through the second flange back into the cylinder, where they are again fed to the combustion process.

Exhaust gas recirculation takes place when the valves in the cylinder are open at the same time. The amount of exhaust gas that returns to the combustion chamber is determined by the electric motor moving the valve disc up and down, opening or closing the outlet flange. This process can be mechanical, electro-pneumatic or electrical.

This is what the EGR valve looks like

EGR valve looks like

The exhaust gas recirculation valve is a rather inconspicuous component. For most manufacturers, the EGR valve is very similar in shape and size to a soda can. On the side facing away from the engine are the connections for the electronics that control the valve. The opposite side is connected to the engine’s combustion chamber. Another connection in the middle of the component is connected to the exhaust manifold.

How the EGR valve is controlled

The electric motor and thus the entire valve is controlled by the onboard electronics on the basis of sensory data on the exhaust gas recirculation sensor, the engine speed and the current power. Another function is the integration of the EGR flap into these complex processes.

The control damper regulates the amount of fresh air entering the engine. In other words, it reduces its inflow depending on the amount of exhaust gas to be “recycled”. In the following article, learn about what is ESP in a car and what to do when it’s on?

Structure and inner workings of the exhaust gas recirculation valve

The interior of the EGR valve housing is called the valve chamber. Inside this chamber is the actual exhaust gas control valve. An electric motor controls a valve rod as required, which runs along the longitudinal axis. At the end of this valve, the rod is a so-called valve disc, which extends to the lower flange and opens or closes it depending on the setting.

Reduced temperature to exhaust gas recirculation

Exhaust gas recirculation systems are reasonably likely to be found on Euro-3 standard diesel vehicles, even more likely on a Euro-4 standard, and certainly on Euro-5 standard diesel. Up to the Euro 4 standard, an exhaust gas control valve may be used. Above that, solutions involving urea are preferred for treating the exhaust gas.

Exhaust gas recirculation via a valve is no longer sufficient for vehicles that are to meet a higher exhaust gas standard than Euro 4 because although it reduces the development of nitrogen oxides, the lower temperature in the combustion chamber brings with it the risk of soot formation, the generation of carbon monoxide and the release of hydrocarbons.

Exhaust gas recirculation would thus only shift one problem to another. As a result, some manufacturers connected the exhaust gas recirculation valve to an exhaust gas recirculation sensor to get around this conflict. This is a lambda sensor that measures the oxygen concentration in the exhaust gas and regulates the fuel supply on the basis of this data.

But even an exhaust gas recirculation sensor does not cleanly resolve the conflict between nitrogen oxide and soot formation to achieve a Euro 5 standard. As a result, vehicles with an emissions standard higher than 4 usually use selective catalytic reduction. Cars with an emissions standard of 3 or lower often have no exhaust treatment beyond a catalytic converter.

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