Page 200 - Understanding Automotive Electronics

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SENSORS AND ACTUATORS 6

Sensors and Actuators

The previous chapter introduced two critically important components
found in any electronic control system: sensors and actuators. This chapter
explains the operation of the sensors and actuators used throughout a modern
car. Special emphasis is placed on sensors and actuators used for power train
(i.e., engine and transmission) applications since these systems normally
employ the largest number of such devices. However, this chapter will also
discuss sensors found in other subsystems on modern cars.
In any control system, sensors provide measurements of important plant
variables in a format suitable for the digital microcontroller. Similarly, actuators
are electrically operated devices that regulate inputs to the plant that directly
control its output. For example, as we shall see, fuel injectors are electrically
driven actuators that regulate the flow of fuel into an engine for engine control
applications.
Recall from Chapter 2 that fundamentally an electronic control system
uses measurements of the plant variable being regulated for feedback control.
The measured variable is compared with a desired value for the variable to
produce an error signal. The electronic controller generates output electrical
signals that regulate inputs to the plant in such a way as to reduce the error to
zero.
As will be shown throughout the remainder of this book, automotive
electronics have many examples of electronic control in virtually every
subsystem. Modern automotive electronic control systems use microcontrollers
based on microprocessors (as explained in Chapter 4) to implement almost all
control functions. Each of these subsystems requires one or more sensors and
actuators in order to operate.
AUTOMOTIVE CONTROL SYSTEM APPLICATIONS OF SENSORS
AND ACTUATORS
In control system applications, sensors and actuators are in many cases the
critical components for determining system performance. This is especially true
for automotive control system applications. The availability of appropriate
sensors and actuators dictates the design of the control system and the type of
function it can perform.
Sensors and actuators The sensors and actuators that are available to a control system designer
play a critical role in are not always what the designer wants, because the ideal device may not be
determining automotive commercially available at acceptable costs. For this reason, often special signal
control system perfor- processors or interface circuits are designed to adapt to an available sensor or
mance. actuator, or the control system is designed in a specific way to fit available

UNDERSTANDING AUTOMOTIVE ELECTRONICS 187