Page 79 - Automotive Engineering Powertrain Chassis System and Vehicle Body

4.1
Chapter 4.1

Digital engine control systems

William Ribbens

4.1.1 Introduction configuration and control concept from one manufac-
turer to another. However, this chapter describes rep-
resentative control systems that are not necessarily based
Traditionally, the term powertrain has been thought to
include the engine, transmission, differential, and drive on the system of any given manufacturer, thereby giving
axle/wheel assemblies. With the advent of electronic the reader an understanding of the configuration and
controls, the powertrain also includes the electronic operating principles of a generic representative system.
control system (in whatever configuration it has). In ad- As such, the systems in this discussion are a compilation
dition to engine control functions for emissions regula- of the features used by several manufacturers.
tion, fuel economy, and performance, electronic controls In fact, most modern engine control systems, such as
are also used in the automatic transmission to select discussed in this chapter, are digital. A typical engine
shifting as a function of operating conditions. Moreover, control system incorporates a microprocessor and is es-
certain vehicles employ electronically controlled clutches sentially a special-purpose computer (or microcontroller).
in the differential (transaxle T/A) for traction control. Electronic engine control has evolved from a relatively
These electronic controls for these major powertrain rudimentary fuel control system employing discrete
components can either be separate (i.e., one for each analog components to the highly precise fuel and ignition
component) or an integrated system regulating the control through 32-bit (sometimes more) microprocessor-
powertrain as a unit. based integrated digital electronic powertrain control.
This latter integrated control system has the benefit of The motivation for development of the more sophisti-
obtaining optimal vehicle performance within the con- cated digital control systems has been the increasingly
straints of exhaust emission and fuel economy regula- stringent exhaust emission and fuel economy regulations.
tions. Each of the control systems is discussed separately It has proven to be cost effective to implement the
beginning with electronic engine control. Then a brief powertrain controller as a multimode computer-based
discussion of integrated powertrain follows. This chapter system to satisfy these requirements.
concludes with a discussion of hybrid vehicle (HV) A multimode controller operates in one of many
control systems in which propulsive power comes from possible modes, and, among other tasks, changes the
an internal combustion engine (ICE) or an electric motor various calibration parameters as operating conditions
(EM) or a combination of both. The proper balance of change in order to optimize performance. To implement
power between these two sources is a very complex multimode control in analog electronics it would be
function of operating conditions and governmental necessary to change hardware parameters (for example,
regulations. via switching systems) to accommodate various operating
conditions. In a computer-based controller, however, the
control law and system parameters are changed via pro-
4.1.2 Digital engine control gram (i.e., software) control. The hardware remains fixed
but the software is reconfigured in accordance with op-
This chapter explores some practical digital control sys- erating conditions as determined by sensor measure-
tems. There is, of course, considerable variation in the ments and switch inputs to the controller.
Understanding Automotive Electronics; ISBN: 9780750675994
Copyright Ó 2003 Elsevier Ltd; All rights of reproduction, in any form, reserved.