Page 231 - Understanding Automotive Electronics

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6 SENSORS AND ACTUATORS

Figure 6.27
Pulse Mode Fuel
Control Signal to Fuel
Injector

FPO

Exhaust Gas Recirculation Actuator
In Chapter 5 it was explained that exhaust gas recirculation (EGR) is
utilized to reduce NO emissions. The amount of EGR is regulated by the
x
engine controller, as explained in Chapter 7. When the correct amount of EGR
has been determined by the controller based on measurements from the various
engine control sensors, the controller sends an electrical signal to the EGR
actuator. Typically, this actuator is a variable-position valve that regulates the
EGR as a function of intake manifold pressure and exhaust gas pressure.
Although there are many EGR configurations, only one representative
example will be discussed to explain the basic operation of this type of actuator.
The example EGR actuator is shown schematically in Figure 6.28. This
actuator is a vacuum-operated diaphragm valve with a spring that holds the
valve closed if no vacuum is applied. The vacuum that operates the diaphragm

218 UNDERSTANDING AUTOMOTIVE ELECTRONICS