Page 31 - Understanding Automotive Electronics

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1 AUTOMOTIVE FUNDAMENTALS

It will be shown in Chapter 7 that ignition timing is actually computed as
a function of engine operating conditions in a special-purpose digital computer
known as the electronic engine control system. This computation of spark
timing has much greater flexibility for optimizing engine performance than a
mechanical distributor and is one of the great benefits of electronic engine
control.

ALTERNATIVE ENGINES
The vast majority of automobile engines in North America are SI engines.
Alternative engines such as the diesel have simply not been able to compete
effectively with the SI engine in the United States. Diesel engines are used
mostly in heavy-duty vehicles such as large trucks, ships, railroad locomotives,
and earth-moving machinery. Because their use in North American passenger
cars is so low and because electronic diesel engine control is not widely used, it
will not be further discussed in this book.
Another alternative to the SI engine has been the Wankel, or rotary,
engine. As in the case of the diesel engine, the number of Wankel engines has
been very small compared to the SI engine. One limitation to its application
has been somewhat poorer exhaust emissions relative to the SI engine.
Probably the most serious competitor to current automotive engines is
the 2-stroke/cycle engine. This engine, which is similar in many respects to
the traditional engine, is a gasoline-fueled, spark-ignited, reciprocating
engine. It has achieved widespread use in lawnmowers, small motorcycles,
and some outboard marine engines. It had (at one time) even achieved
limited automotive use, though it suffered from poor exhaust emissions.
Just as in the case of the 4-stroke/cycle engine, electronic controls have
significantly improved 2-stroke/cycle engine performance relative to
mechanical controls. After considerable research and development, a version of
the 2-stroke/cycle engine is emerging that has great potential for displacing the
4-stroke/cycle engine in automotive applications. It remains to be seen what
inroads the 2-stroke/cycle engine will make.

DRIVETRAIN
The engine drivetrain system of the automobile consists of the engine,
transmission, drive shaft, differential, and driven wheels. We have already
discussed the SI engine and we know that it provides the motive power for the
automobile. Now let’s examine the transmission, drive shaft, and differential in
order to understand the roles of these devices.
Transmission

The transmission is a gear system that adjusts the ratio of engine speed
to wheel speed. Essentially, the transmission enables the engine to operate

18 UNDERSTANDING AUTOMOTIVE ELECTRONICS