Page 27 - Understanding Automotive Electronics

2735 | CH 1 Page 14 Tuesday, March 10, 1998 10:52 AM

1 AUTOMOTIVE FUNDAMENTALS

Before the advent of modern electronic controls, the distribution of
high-voltage pulses was accomplished with a rotary switch called the
distributor. Figure 1.9 shows a schematic of a typical distributor; Figure 1.10
is a typical physical layout. The center electrode is mechanically driven by the
camshaft (via gears) and rotates synchronously at camshaft speed (i.e., one-
half of crankshaft speed). The distributor is an obsolete means for
distribution of the spark to the appropriate spark plug, and is being replaced
by multiple coils, typically one each for a pair of cylinders, as explained in
Chapter 7.
Once again, as in the case of fuel delivery, we explain spark distribution in
terms of the distributor and spark initiation in terms of breaker points in order
to provide a framework for the discussion of the modern distributorless ignition
systems. In this way the reader can see the benefits of the electronic controls.

Figure 1.10
Distributor

FPO

14 UNDERSTANDING AUTOMOTIVE ELECTRONICS