Systems related to engine management and emission control include the following:
- a) On-Board Diagnostic System (OBD) - see Chapter 5;
- b) Electronic engine management system (ECM) — see chapter 5;
- c) Controlled crankcase ventilation system (PCV);
- d) Exhaust gas recirculation system (EGR);
- e) Evaporative Emission System (EVAP);
- f) Catalytic converter and lambda probe (exhaust gas composition control).
The following sections provide general descriptions of how each system works.
Diagnostics of elements of toxicity reduction systems controlled by electronic devices requires the use of special, difficult-to-use equipment and a certain qualification of the performer, and therefore, it would be reasonable to entrust its implementation to professional mechanics of a specialized service station. The foregoing does not mean that the maintenance and repair of components of toxicity reduction systems in practice seem difficult. Do not forget that one of the most common causes of failures is an elementary violation of the quality of vacuum or electrical connections, and therefore, first of all, you should always check the condition of the fittings and electrical connectors. The car owner can independently and quite simply carry out a number of checks, as well as perform many routine maintenance procedures for most system components at home, using the usual set of tuning and locksmith tools.
Crankcase ventilation system (PCV)
The PCV system is used to reduce the emission of hydrocarbon compounds into the atmosphere by removing crankcase gases from the engine. The unit is purged by forcing fresh air coming from the air cleaner through the crankcase, where it mixes with accumulated fumes and gases escaping from the combustion chambers and is discharged through the PCV valve into the intake manifold.
The main components of the system are the PCV valve, the purge filter and the set of vacuum hoses connecting these devices to the engine.
In order to maintain stable idle speed, the PCV valve shuts off the purge flow when the vacuum in the intake manifold is deep. In the event of a malfunction of the engine (such as worn piston rings) the system removes excess crankcase gases through the ventilation tube back to the air cleaner.
Exhaust gas monitoring
See also Chapter «Controls and methods of operation», Section 28.
In order to minimize the emission of toxic components into the atmosphere, a catalytic converter is included in the exhaust gas system. The control is carried out by a closed type control system. Feedback from the engine management system is organized by means of a lambda probe mounted in the exhaust pipe of the exhaust system.
The catalytic converter is a component of exhaust gas toxicity reduction systems, is included in the exhaust system and serves to reduce the emission of toxic components into the atmosphere. The vehicles covered in this manual use two types of catalytic converters. A conventional oxidizing converter can reduce the content of hydrocarbons and carbon monoxide in the exhaust gases. Tri-functional catalytic converter further reduces nitrogen oxide emissions (NOx).
Lambda probe (oxygen sensor) monitors the oxygen content in the exhaust gas stream. Upon contact of O molecules2 with a sensitive element of the probe, the sensor generates an amplitude signal depending on the oxygen concentration. The electronic module of the engine management system continuously monitors the signals coming from the lambda probe, if necessary, issuing commands to adjust the composition of the air-fuel mixture by changing the duration of the opening of the injection injectors. On the car models in question, two lambda probes are used; the primary is located in the exhaust manifold of the engine, and the secondary is located below the catalytic converter. By comparing the level of oxygen in the sections of the exhaust tract above and below the catalytic converter, the engine management system also determines the efficiency of the latter.
Evaporative Emission System (EVAP)
The system accumulates vapors accumulated in the fuel tank and ensures that they are discharged into the intake manifold for combustion during normal engine operation. The general principle of operation of the EVAP system is described below. The described design does not have to fully correspond to the design of the system installed on a particular vehicle, however, the principle of operation is common to all models.
Any EVAP system necessarily includes a special adsorber filled with activated carbon, which, in fact, collects fuel vapors. The method of removing vapor from the adsorber may vary depending on the design of a particular system.
The fuel filler cap is equipped with a two-way safety valve. In the event of a system failure, the valve ensures that fuel vapors are vented to the atmosphere. Other check valve (ORVR valve) installed near the fuel tank and provides adjustment of fuel vapor removal to the carbon adsorber depending on pressure/vacuum drops associated with temperature changes.
On the way to the carbon adsorber, fuel vapors are passed through a two-way valve and through the ventilation hoses they enter the carbon adsorber installed in the engine compartment, where they accumulate while the car engine is turned off.
When the engine is started until it warms up to a certain temperature, the canister purge shut-off solenoid valve remains closed. From the adsorber, fuel vapors are blown out through the diaphragm valve into the intake manifold, from where they enter the combustion chambers, where they are burned out during the normal operation of the engine. The fuel tank is also usually equipped with a sensor that monitors pressure changes in the tank both while the vehicle is stationary and while the vehicle is moving.
Exhaust gas recirculation system
In order to reduce the emission of nitrogen oxides into the atmosphere (NOx) the design of the engine provides for the removal of part of the exhaust gases into the intake pipeline through the EGR valve. This admixture of exhaust gases to the air-fuel mixture leads to a decrease in its combustion temperature.
The system consists of an EGR valve, an EGR valve opening degree sensor and a set of auxiliary information sensors. The system is controlled by the electronic module of the engine control system. The module controls the optimal degree of opening of the EGR valve for any engine operating conditions. A special information sensor constantly monitors the degree of opening of the EGR valve, issuing appropriate signals to the control module. The electronic device compares the incoming information of the sensor with the optimal calculated value determined from the data coming from other information sensors and, if necessary, makes the required adjustment of the volume of exhaust gases entering the engine.
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