Page 168 - Understanding Automotive Electronics

2735 | CH 5 Page 155 Tuesday, March 10, 1998 11:10 AM

THE BASICS OF ELECTRONIC ENGINE CONTROL 5

Figure 5.4
Generic Electronic
Engine Control FPO
System

As explained in Chapter 2, a closed-loop control system requires
measurements of certain variables that tell the controller the state of the system
being controlled. The electronic engine control system receives input electrical
signals from the various sensors that measure the state of the engine. From
these signals, the controller generates output electrical signals to the actuators
that determine the engine calibration (i.e., correct fuel delivery and spark
timing).
Examples of automotive engine control system sensors will be discussed in
Chapter 6. As mentioned, the configuration and control for an automotive
engine control system are determined in part by the set of sensors that is
available to measure the variables. In many cases, the sensors available for
automotive use involve compromises between performance and cost. In other
cases, only indirect measurements of certain variables are feasible. From
measurement of these variables, the desired variable is found by computation.
Overall engine func- Figure 5.5 identifies the automotive functions that surround the engine.
tions that are subject to There is a fuel metering system to set the air–fuel mixture flowing into the engine
electronic engine con- through the intake manifold. Spark control determines when the air–fuel mixture
trols are air/fuel ratio, is ignited after it is compressed in the cylinders of the engine. The power is
spark control, and delivered at the driveshaft, and the gases that result from combustion flow out of
exhaust gas recirculation. the exhaust system. In the exhaust system, there is a valve to control the amount
of exhaust gas being recirculated back to the input, and a catalytic converter to
further control emissions. This addition to the engine, as well as various sensors
and actuators depicted in Figure 5.5, is explained later.
At one stage of development, the electronic engine control consisted of
separate subsystems for fuel control, spark control, and exhaust gas recirculation.
The ignition system in Figure 5.5 is shown as a separate control system, although
engine control is evolving toward an integrated digital system (see Chapter 7).
This chapter discusses the various electronic engine control functions
separately and explains how each function is implemented by a separate control
system. Chapter 7 shows how these separate control systems are being
integrated into one system.

UNDERSTANDING AUTOMOTIVE ELECTRONICS 155