All diesel models are also designed to meet the most stringent emission standards. They are also equipped with a crankcase ventilation system. Many engines are equipped with a catalytic converter and an exhaust gas recirculation system to further reduce harmful emissions (EGR).
Emission control systems operate as described below.
Petrol engine models
Engine ventilation system
To reduce the release of unburned hydrocarbons from the crankcase into the atmosphere, the engine is sealed. Blow-by gases and oil vapors are drawn out of the engine crankcase, pass through the oil-separating wire mesh and are introduced into the intake tract. After that, they burn in the engine along with the fuel in the usual way.
In conditions of high vacuum in the intake manifold (idling deceleration) gases will be forced to be sucked from the crankcase. Under low vacuum conditions (acceleration, wide open throttle operation) gases are removed from the crankcase under the influence of (relatively) higher crankcase pressure. If the engine is worn, increased crankcase pressure (due to increased gas breakthrough) under all conditions of depression in the manifold will cause some of the gases to return.
Exhaust emission reduction
To minimize the amount of pollutants released into the atmosphere, all models are equipped with a catalytic converter located in the exhaust system. System - closed type (with feedback). One or two oxygen sensors located in the exhaust system provide feedback to the engine control unit, allowing it to adjust the air/fuel mixture to provide the best possible catalyst performance.
Each oxygen sensor (Lambda probe) has a built-in heating element, which is controlled by the ECU using the appropriate relay and serves to quickly heat the sensor tip to an effective operating temperature. The tip of the oxygen sensor is sensitive to oxygen and, depending on the amount of oxygen in the exhaust gases, sends an alternating voltage signal to the ECU. The leaner the air-fuel mixture, the higher the oxygen content and the lower the signal voltage from the sensor. If the air-fuel mixture is too rich, the oxygen content in the exhaust gases is low and therefore the sensor sends out a higher voltage signal. The maximum conversion efficiency of all major pollutants is observed if the ratio «air-fuel» maintained in the chemically correct ratio (ensuring complete combustion of gasoline) at 14.7 parts air to 1 part fuel (by weight) (so-called «stoichiometric» ratio). In this «point» the output voltage of the sensor changes dramatically. The BEU, using the change in the signal as a reference point, adjusts the composition of the air-fuel mixture accordingly by changing the pulse duration of the fuel injectors.
Fuel vapor recovery
To minimize the release of unburned hydrocarbons into the atmosphere, a fuel vapor recovery system is used. The fuel filler cap is sealed, and an adsorber is installed in the engine compartment under the right front fender. The adsorber collects gasoline vapors generated in the tank when the car is parked and stores them until it can be removed from the adsorber (under the control of the BEU engine) through the purge valve into the intake tract. After that, they should burn in the engine in the usual way along with the fuel.
To ensure proper operation of a cold engine and / or engine idling and protect the catalytic converter from the influence of a rich mixture, the valve (-s) purge control does not open the ECU until the engine is warm and under load. The valve solenoid then cycles on and off periodically, allowing the accumulated steam to pass into the intake tract.
Secondary Air Injection Some later engines that meet the L4 emission standard are also equipped with a secondary air injection system. This system is designed to reduce exhaust emissions between the first engine start and until the catalytic converter reaches operating temperature. The injection of air into the exhaust system during the initial start-up period creates the effect «afterburning», which allows you to quickly increase the temperature in the downpipe of the exhaust system, thus bringing the catalytic converter to normal operating temperature very quickly.
The system consists of an air pump, an air injection valve and connecting air hoses.
The system operates for 10-45 seconds after starting the engine, depending on the temperature of the coolant.
Diesel Models
Engine ventilation system
See items 4-5.
Exhaust emission reduction
To minimize the amount of pollutants released into the atmosphere, the exhaust system on some later models is equipped with a catalytic converter.
The catalytic converter consists of a housing containing a cellular filler impregnated with catalytic material, through which the hot exhaust gases pass. The catalyst accelerates the oxidation of harmful carbon monoxide, unburned hydrocarbons and soot, effectively reducing the amount of harmful products released into the atmosphere with exhaust gases.
Exhaust gas recirculation system (EGR)
This system is designed to recirculate a small amount of exhaust gases into the intake tract and, therefore, to involve them in the combustion process. As a result, the level of nitrogen oxides in the exhaust gases released into the atmosphere decreases.
The amount of exhaust gas recirculation is controlled by vacuum generated by the vacuum pump of the brake booster and transmitted through a solenoid valve controlled by the preheating system or an electronic control unit.
A valve is located on the exhaust manifold to control the amount of recirculated exhaust gases. The valve is actuated by a vacuum applied through a solenoid valve.
In addition, on some models, a throttle valve is installed in the intake manifold to control the ratio between air and recirculated exhaust gases. The throttle also allows exhaust gases to be drawn into the intake manifold at idle or under light load when the valve on the exhaust manifold is fully open.
The system is controlled by an electronic control unit that receives information about the coolant temperature, load and engine speed respectively from the coolant temperature switch sensor, throttle position switch sensor and crankshaft sensor.