The non-adjustable catalytic converter converts the carbon monoxide and hydrocarbon compounds contained in the exhaust gas into carbon dioxide (CO 2) and water (H2 O). Air required by the catalyst for combustion (oxidation) carbon monoxide and hydrocarbons comes from the turbocharger. The catalyst itself consists of a honeycomb ceramic monolith coated with a thin layer of precious metals (see illustration 3.0).
High content of nitrogen oxides (NOx) in the exhaust gases is reduced as a result of the operation of the exhaust gas recirculation system. The system is based on valves through which part of the exhaust gases is diverted back to the intake manifold, and from there to the combustion chambers. The volume of these gases is regulated and depends on the operating load on the engine. In view of the fact that 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 lowering the level of nitrogen oxides.
Due to the fact that the flow of exhaust gases back into the intake manifold is only necessary from the moment the engine starts to work with a load, the recirculation process is regulated by a whole chain of controls. The main one is the electromagnetic two-way EGR valve, which operates on 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 the vacuum pump.
The partial load switch, located on the injection pump, ensures that part of the exhaust gases returns to the intake manifold only at the moment when the accelerator pedal is pressed.
The coolant temperature sensor sends an appropriate signal about the current coolant temperature. When the engine is cold, when the temperature of the coolant does not exceed 50°C, exhaust gases are not needed.
From terminal «W» generator receives a signal of the number of revolutions. Above 1200 rpm, the exhaust gas recirculation is interrupted for two seconds. If the engine speed reaches 3200 rpm, the exhaust gas recirculation is switched off (see illustration 3.0a).
The high-altitude corrector of the electronic control unit for the recirculation system turns off the recirculation system when driving at an altitude of approximately 1000 m above sea level.
The electronic control unit for the recirculation system, depending on the information received, gives the appropriate command to the EGR solenoid valve. The control unit is located under No. 14 on the additional relay block under the instrument panel on the left side. Recently functional «responsibilities» control unit expanded by installing a sensor for increasing idle speed (for vehicles with air conditioning). The block and the specified sensor are combined in one housing and are located at numbers 13 and 14 on the block of additional relays (see arrow in illustration 3.0b).
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