Page 160 - Understanding Automotive Electronics

2735 | CH 5 Page 147 Tuesday, March 10, 1998 11:10 AM

THE BASICS OF ELECTRONIC ENGINE CONTROL 5

The Basics of Electronic

Engine Control

Engine control in the vast majority of engines means regulating fuel and
air intake as well as spark timing to achieve desired performance in the form of
torque or power output. Until the late 1960s, control of the engine output
torque and RPM was accomplished through some combination of mechanical,
pneumatic, or hydraulic systems. Then, in the 1970s, electronic control systems
were introduced.
This chapter is intended to explain, in general terms, the theory of
electronic control of the automotive engine. Chapter 7 explains practical
control methods and systems. The examples used to explain the major
developments and principles of electronic control have been culled from the
techniques used by various manufacturers and are not necessarily representative
of any single automobile manufacturer at the highest level of detail.
MOTIVATION FOR ELECTRONIC ENGINE CONTROL
The motivation for electronic engine control came in part from two
government requirements. The first came about as a result of legislation to
regulate automobile exhaust emissions under the authority of the
Environmental Protection Agency (EPA). The second was a thrust to improve
the national average fuel economy by government regulation.
Exhaust Emissions

The combustion of gaso- The engine exhaust consists of the products of combustion of the air and
line in an engine results gasoline mixture. Gasoline is a mixture of chemical compounds that are called
in exhaust gases includ- hydrocarbons. This name is derived from the chemical formation of the various
ing CO , H O, CO, gasoline compounds, each of which is a chemical union of hydrogen (H) and
2
2
oxides of nitrogen, and carbon (C) in various proportions. Gasoline also contains natural impurities as
various hydrocarbons. well as chemicals added by the refiner. All of these can produce undesirable
exhaust elements.
During the combustion process, the carbon and hydrogen combine with
oxygen from the air, releasing heat energy and forming various chemical
compounds. If the combustion were perfect, the exhaust gases would consist
only of carbon dioxide (CO ) and water (H O), neither of which are
2
2
considered harmful in the atmosphere. In fact, both are present in a human’s
breath.

UNDERSTANDING AUTOMOTIVE ELECTRONICS 147