In-Vehicle Computers

Automotive marketing research firm Auto-Pacific lists 65 features available in today's automobiles, that use computers—in addition to the microprocessors used in standard features. Even a new car in the lowest price tier with no extra features is equipped with about 30 computers, and at the other end of the spectrum, every function of a vehicle can be computer-assisted or monitored. In-vehicle computers are used in devices such as Global Positioning System data receivers, satellite radio, drowsiness alert systems, and Volvo's City Safety system, which prevents the car from tailgating.

In-vehicle computers were developed in the early years of the computer industry in the late 1960s and early 1970s, both by computer designers hoping to attract automobile manufacturers as customers and by in-house departments in automobile companies. General Motors, for instance, created the Electronic Control Systems Department in 1971.

Even before the introduction of the first major home computers in the early 1980s, 4-bit microprocessors were incorporated into car designs with cruise control, traction control, and antilock brake control. Other functions followed, made possible by in-vehicle computers: digital speedometers and trip mileage counters, speed warning systems, automatic door locks, and engine control features like ignition spark advance and dwell controls. By 1980, microprocessors were in use to improve emissions systems.

Today, in-vehicle computers are called electronic control units. While early microprocessors used compact, efficient algorithms because of the memory and processing constraints imposed by the technology of the time, systems in today's automobiles may use as many as 100 million lines of code. Some of these systems exist simply to protect against malfunction in other systems, for instance, safeguarding against the effects of electronic interference and preventing sudden braking or acceleration in the event of a system shorting out. This code is sometimes called “defensive programming.”

One of the key electronic control units is the engine control unit (sometimes subsumed into a powertrain control module, which also includes a transmission control unit). The engine control unit is responsible for optimizing the performance of a car's internal combustion engine by adjusting the engine's actuators in response to conditions, replacing the older means of using mechanical and pneumatic systems to adjust air/fuel mixture, idle speed, and ignition timing. The idea of an engine control unit considerably predates the use of in-vehicle computers, but it was the use of microprocessors in automobiles that allowed the vision of early engineers to be effectively realized.

Though many manufacturers have proprietary systems in their vehicles, basic descriptive terms tend to describe a class of electronic control units. Airbag control units, for instance, govern the functioning of the airbag feature, while seat control units govern seat functions. Body control modules govern and monitor the electronic systems in the body of the car, from power window and power mirror systems to air conditioning to the immobilizer. The various systems of the car communicate with each other by means of the vehicle bus, which also includes the on-board diagnostics (OBD) connector, required in all American automobiles since 1996. Bus in this case is a computing term for a [Page 856]system responsible for handling data transfers and other functions between systems either within a computer or among multiple computers.

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