Car Computers

Each year, cars seem to get more and more complicated. Cars
today might have as many as 50 microprocessors on them.
Although these microprocessors make it more difficult for you
to work on your own car, some of them actually make your car
easier to service.

Some of the reasons for this increase in the number of
microprocessors are:

* The need for sophisticated engine controls to meet
emissions and fuel-economy standards
* Advanced diagnostics
* Simplification of the manufacture and design of cars
* Reduction of the amount of wiring in cars
* New safety features
* New comfort and convenience features

In this article, we'll take a look at how each of these
factors has influenced the design of your car.

Sophisticated Engine Controls

Before emissions laws were enacted, it was possible to build a
car engine without microprocessors. With the enactment of
increasingly stricter emissions laws, sophistic­ated control
schemes were needed to regulate the air/fuel mixture so that
the catalytic converter could remove a lot of the pollution
from the exhaust.

Controlling the engine is the most processor-intensive job on
your car, and the engine control unit (ECU) is the most
powerful computer on most cars. The ECU uses closed-loop
control, a control scheme that monitors outputs of a system
to control the inputs to a system, managing the emissions and
fuel economy of the engine (as well as a host of other
parameters). Gathering data from dozens of different sensors,
the ECU knows everything from the coolant temperature to the
amount of oxygen in the exhaust. With this data, it performs
millions of calculations each second, including looking up
values in tables, calculating the results of long equations
to decide on the best spark timing and determining how long
the fuel injector is open. The ECU does all of this to ensure
the lowest emissions and best mileage. See How Fuel Injection
Systems Work for a lot more detail on what the ECU does.

A modern ECU might contain a 32-bit, 40-MHz processor. This
may not sound fast compared to the 500- to 1,000-MHz
processor you probably have in your PC, but remember that the
processor in your car is running much more efficient code
than the one in your PC. The code in an average ECU takes up
less than 1 megabyte (MB) of memory. By comparison, you
probably have at least 2 gigabytes (GB) of programs on your
computer -- that's 2,000 times the amount in an ECU.