Page 201 - Understanding Automotive Electronics

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6 SENSORS AND ACTUATORS

sensors or actuators. However, because of the large potential production run for
automotive control systems, it is often worthwhile to develop a sensor for a
particular application, even though it may take a long and expensive research
project to do so.
Although there are many subsystems on automobiles that operate with
sensors and actuators, we begin our discussion with a survey of the devices for
power train control. To motivate the discussion of engine control sensors and
actuators it is helpful to review the variables measured (sensors) and the
controlled variables (actuators). Figure 6.1 is a representative block diagram of a
typical electronic engine control system illustrating most of the relevant sensors
used for engine control. The position of the throttle plate, sensed by the
throttle position sensor (TPS), directly regulates the air flow into the engine,
thereby controlling output power. A set of fuel injectors (one for each cylinder)
delivers the correct amount of fuel to a corresponding cylinder during the
intake stroke under control of the electronic engine controller. A fuel injector
is, as will presently be shown, one of the important actuators used in
automotive electronic application. The ignition control system fires each spark
plug at the appropriate time under control of the electronic engine controller.
The exhaust gas recirculation (EGR) is controlled by yet another output from
the engine controller. All critical engine control functions are based on
measurements made by various sensors connected to the engine in an
appropriate way. Computations made within the engine controller based on
these inputs yield output signals to the actuators. We consider inputs (sensors)
to the control system first, then we will discuss the outputs (actuators).

Figure 6.1
Typical Electronic Engine Control System

188 UNDERSTANDING AUTOMOTIVE ELECTRONICS