Exhaust Gas Recirculation System — General Information (Peugeot Eurovans 807)

High levels of nitrogen oxides (NOx) in the exhaust gases are reduced by the exhaust gas recirculation system. The basis of the system is the valves through which part of the exhaust gases is diverted back into the intake manifold and from there into the combustion chambers. The volume of these gases is regulated and depends on the operating load on the engine. Since these gases contain almost nothing that could burn, they do not burn, but this allows for a reduction in the volume of fresh air supplied and at the same time reduces the temperature in the combustion chambers, thereby reducing the level of nitrogen oxides.

Since the supply of exhaust gases back to the intake manifold is only necessary from the moment the engine begins to operate under load, the recirculation process is regulated by a whole link of control elements. The main valve is the electromagnetic exhaust gas recirculation valve, which operates on reduced pressure and is controlled by a microprocessor. A vacuum pump generates reduced pressure for the mechanical recirculation valve.

The reference signal for the gasoline engine control unit to divert part of the exhaust gas into the combustion chambers is the information from the coolant temperature sensor. When the engine is cold, when the coolant temperature does not exceed 60°C, exhaust gas drainage is not required. On vehicles with a diesel engine, signals from the mass air flow sensor and the crankshaft speed sensor are used as reference signals (see illustrations 6.0, 6.0a). When switching the exhaust gas recirculation system on and off, the engine control unit also uses the parametric data stored in its memory based on the engine load, which in turn is determined by the position of the accelerator pedal.

6.0. Functional diagram of the exhaust gas recirculation system of a vehicle with a gasoline engine 1 - intake manifold; 2 - electromagnetic valve of exhaust gas recirculation; 3 - thermostat housing with coolant temperature sensor; 4 - exhaust gas pipe with mechanical valve; 5 - valve on the intake manifold inlet pipe; 6 - intake manifold; 7 - cylinder head

6.0a. Main components of the exhaust gas recirculation system of a diesel vehicle 1 - mass air flow sensor; 2 - crankshaft speed/position sensor; 3 - engine control unit; 4 - EGR valve; 5 - intake manifold flap; 6 - electromagnetic valve of the intake manifold flap; 7 - electromagnetic valve of the exhaust gas recirculation system

The arrows show the direction of movement of exhaust gases diverted for afterburning.

The solenoid valve consists of a winding and a magnetic core that attracts the valve, as well as a potentiometer that registers the valve position (see illustration 6.0b).