Page 200 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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184 Automobile mechanical and electrical systems

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Figure 2.211 Exhaust gas recirculation (EGR) system: 1, vacuum actuator; 2, sensor;
3, vacuum control valve; 4, lambda sensor; 5, catalytic converter; 6, electronic control
module (ECM)

through the fi lter in the opposite direction. The air collects the deposited fuel
vapour and carries it through pipes into the inlet manifold and engine, where it is
burnt. To prevent vapour loss through this route when the engine is not running, a
canister purge control valve is fi tted into the fuel vapour line. The valve is closed
when the engine is stationary and during warm-up. When the engine is at normal
running temperature the valve opens and the inlet manifold vacuum is able to
cause air fl ow through the canister. This draws vapour out of the fi lter and into
the inlet manifold.
The evaporative canister can be fi tted almost anywhere on the vehicle. It may
be near to the fuel tank, in the engine compartment or under a body panel.

Fuel traps, to prevent fuel loss if the vehicle turns over in an accident, are
also fi tted.

2.4.6.3 Exhaust gas recirculation
Exhaust gas recirculation (EGR) has become a common feature on petrol and
diesel engines ( Fig. 2.211 ). The addition of exhaust gas to a fresh air and fuel
Key fact charge lowers the combustion temperature and reduces the formation of NOx.
The addition of exhaust gas to a fuel/ EGR operates during normal engine temperature and high vacuum conditions.
air charge lowers the combustion Exhaust gases are piped from the exhaust manifold to the inlet manifold through
temperature and reduces the a vacuum or electrically operated valve.
formation of nitrogen oxides.
The amount of exhaust gas introduced into the air supply is usually less than
15% of the total charge. However, where closed-loop control is used, up to 50%
can be used under some conditions on diesel engine systems. Some systems
use a one-piece electrical solenoid valve, in place of the separate electronic
vacuum regulator and valve. Some valves have a sensor fi tted above the valve so
that the ECM can monitor the opening performance.

Key fact
2.4.7 Turbocharging and supercharging
Superchargers are driven from the
engine crankshaft. Supercharging is a method of increasing the performance of internal combustion
engines by boosting the air charge with an air pump. The most popular method
is turbocharging, as this uses some of the lost energy in the exhaust gas fl ow