Page 166 - Understanding Automotive Electronics

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THE BASICS OF ELECTRONIC ENGINE CONTROL 5

describe an engine can be changed easily by changing data stored in the system’s
computer memory.
Additional Cost Incentive

Dropping costs of Besides providing control accuracy and stability, there is a cost incentive
microprocessors and to use digital electronic control. The system components—the multifunction
other very large scale digital integrated circuits—are decreasing in cost, thus decreasing the system
integrated circuits have cost. From about 1970 on, considerable investment was made by the
made electronic engine semiconductor industry for the development of low-cost, multifunction
control an increasingly integrated circuits. In particular, the microprocessor and microcomputer have
attractive system for reached an advanced state of capability at relatively low cost. This has made the
automobile manufac- electronic digital control system for the engine, as well as other on-board
turers. automobile electronic systems, commercially feasible.
As pointed out in Chapter 3, as multifunction digital integrated circuits
continue to be designed with more and more functional capability through very
large scale integrated circuits (VLSI), the costs continue to decrease. At the
same time, these circuits offer improved electronic system performance in the
automobile.
In summary, the electronic engine control system duplicates the function
of conventional fluidic control systems, but with greater precision. It can
optimize engine performance while meeting the exhaust emission and fuel
economy regulations and can adapt to changes in the plant.

CONCEPT OF AN ELECTRONIC ENGINE CONTROL SYSTEM
In order to understand electronic engine control it is necessary to
understand some fundamentals of how the power produced by the engine is
controlled. Any driver understands intuitively that the throttle directly regulates
the power produced by the engine at any operating condition. It does this by
controlling the air flow into the engine.
In essence the engine is an air pump such that at any RPM the mass flow
rate of air into the engine varies directly with throttle plate angular position (see
Figure 5.3).
As the driver depresses the accelerator pedal, the throttle angle (θ in
Figure 5.3) increases, thereby allowing an increased air flow into the engine.
The role of fuel control is to regulate the fuel that is mixed with the air so that
it increases in proportion to the air flow. As we will see later in this chapter,
the performance of the engine is affected strongly by the mixture (i.e., by the
ratio of air to fuel). However, for any given mixture the power produced by
the engine is directly proportional to the mass flow rate of air into the engine.
In the U.S. system of units, an air flow rate of about 6 lb/hr produces 1
horsepower of usable mechanical power as the output of the engine. Metric

UNDERSTANDING AUTOMOTIVE ELECTRONICS 153