Page 91 - Automotive Engineering Powertrain Chassis System and Vehicle Body

Digital engine control systems CHAPTER 4.1

ROM LOOK-UP TABLE

MAF
SA S SA P SA T
A/B
POS/RPM
CONTROLLER
D/B
CT

TPS

TRIGGER
ELECTRONIC PULSES DRIVER
IGNITION
CIRCUITRY
SYSTEM
P 1 P 2
SPARK
PLUGS
S 1 S 2

Fig. 4.1-9a Distributorless ignition system.

control (i.e., the controller that regulates fuel). This
system receives data from the various sensors (as
described above with respect to fuel control) and
determines the correct SA for the instantaneous operat-
ing condition.
The variables that influence the optimum spark timing
at any operating condition include RPM, manifold pres-
sure (or MAF), barometric pressure, and CT. The correct
ignition timing for each value of these variables is stored
in an ROM lookup table. For example, the variation of
SA with RPM for a representative engine is shown in
Fig. 4.1-9b. The engine control system obtains readings
from the various sensors and generates an address to the
lookup table (ROM). After reading the data from the
Fig. 4.1-9b Spark advance versus RPM. lookup tables, the control system computes the correct
SA. An output signal is generated at the appropriate time
to activate the spark.
engine configuration from studies of engine performance In the configuration depicted in Fig. 4.1-9a, the elec-
as measured on an engine dynamometer. tronic ignition is implemented in a stand-alone ignition
Fig. 4.1-9a is a schematic of a representative electronic module. This solid-state module receives the correct SA
ignition system. In this example configuration the spark data and generates electrical signals that operate the coil
advance (SA) value is computed in the main engine driver circuitry. These signals are produced in response to

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