The unregulated catalytic converter converts carbon monoxide and hydrocarbon compounds contained in the exhaust gas into carbon dioxide (CO₂) and water (H₂ O). The air required by the catalytic converter to burn (oxidize) the carbon monoxide and hydrocarbons comes from the turbocharger. The catalytic converter itself consists of a honeycomb ceramic monolith coated with a thin layer of precious metals (see illustration 3.0).
The high content of nitrogen oxides (NOx) in the exhaust gases is reduced by the exhaust gas recirculation system. The system is based on 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. However, this reduces 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 starts to operate under load, the recirculation process is regulated by a whole link of control elements. The main one is the electromagnetic two-way exhaust gas recirculation valve, which operates from reduced pressure and is controlled by the electronic unit of the exhaust gas recirculation system. The reduced pressure for the mechanical recirculation valve is generated by a vacuum pump.
The partial load switch, located on the high-pressure fuel pump, ensures that part of the exhaust gases are returned to the intake manifold only when the accelerator pedal is pressed.
The coolant temperature sensor sends a corresponding signal about the current coolant temperature. When the engine is cold, when the coolant temperature does not exceed 50°C, the exhaust gas outlet is not required.
The generator terminal "W" receives a speed signal. At engine speeds above 1200 rpm, EGR is interrupted for two seconds. If the engine speed reaches 3200 rpm, EGR is switched off (see illustration 3.0a).
The altitude corrector of the electronic control unit of the recirculation system switches off the recirculation system when driving at an altitude of approximately 1000 m above sea level.
The electronic control unit of the recirculation system, depending on the received information, sends a corresponding command to the electromagnetic valve of the exhaust gas recirculation. The control unit is located under No.14 on the block of additional relays under the instrument panel on the left side. Recently, the functional "responsibilities" of the control unit have been expanded by installing an idle speed increase sensor (for cars with air conditioning). The block and the specified sensor are combined in one housing and are located under numbers 13 and 14 on the block of additional relays (see arrow in illustration 3.0b).
