Page 232 - Understanding Automotive Electronics

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SENSORS AND ACTUATORS 6

Figure 6.28
EGR Actuator Control

FPO

is supplied by the intake manifold and is controlled by a solenoid-operated
valve. This solenoid valve is controlled by the output of the control system.
One kind of EGR actua- This solenoid operates essentially the same as that explained in the
tor consists of a vacuum- discussion on fuel injectors. Whenever the solenoid is energized (i.e., by current
operated valve with the supplied by the control system flowing through the coil), the EGR valve is
vacuum supply con- opened by the applied vacuum.
trolled by a solenoid. The amount of valve opening is determined by the average pressure on
When the EGR valve is the vacuum side of the diaphragm. This pressure is regulated by pulsing the
open, exhaust gas flows solenoid with a variable-duty-cycle electrical control current. The duty cycle
into the intake manifold. (see discussion on fuel injectors) of this pulsing current controls the average
pressure in the chamber that affects the diaphragm deflection, thereby
regulating the amount of EGR.
Ignition System
The equivalent of an actuator for the ignition system on an engine is the
combination of the spark plug, the ignition coil, and driver electronic circuits.

UNDERSTANDING AUTOMOTIVE ELECTRONICS 219