Page 165 - Understanding Automotive Electronics

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5 THE BASICS OF ELECTRONIC ENGINE CONTROL

Standards have been written for the vehicle half-life (5 years or 50,000
miles—whichever comes first) and full life cycle (10 years or 100,000 miles).
The standards are:

HC 0.31 g/mi
CO 4.20 g/mi
NO x 0.60 g/mi (nondiesel)
1.25 g/mi (diesel)
These regulations were phased in according to the following schedules:

Model year 1994: 40%
Model year 1995: 80%
Model year 1996: 100%

There are many details to these regulations that are not relevant to the
present discussion. However, the regulations themselves are important in that
they provided motivation for expanded electronic controls.

Meeting the Requirements

Engines using mechani- Unfortunately, as seen later in this chapter, meeting the government
cal, hydraulic, or pneu- regulations causes some sacrifice in performance. Moreover, attempts to
matic controls cannot meet the Table 5.1 standards using mechanical, electromechanical,
meet government regula- hydraulic, or pneumatic controls like those used in pre–emission control
tions, but engines using vehicles have not been cost effective. In addition, such controls cannot
electronic engine con- reproduce functions with sufficient accuracy across a range of production
trols can. vehicles, over all operating conditions, and over the life of the vehicle to stay
within the tolerance required by the EPA regulations. Each automaker must
verify that each model produced will still meet emission requirements after
traveling 50,000 miles. As in any physical system, the parameters of
automotive engines and associated peripheral control devices can change
with time. An electronic control system has the ability to automatically
compensate for such changes and to adapt to any new set of operating
conditions.

The Role of Electronics
The use of digital electronic control has enabled automakers to meet the
government regulations by controlling the system accurately with excellent
tolerance. In addition, the system has long-term calibration stability. As an
added advantage, this type of system is very flexible. Because it uses
microcomputers, it can be modified through programming changes to meet a
variety of different vehicle/engine combinations. Critical quantities that

152 UNDERSTANDING AUTOMOTIVE ELECTRONICS