How Car Computers Work

在排放法律颁布之前,it was possible to build acar enginewithoutmicroprocessors. 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. (SeeHow Catalytic Converters Workfor more details.)

Controlling theengineis the most processor-intensive job on your car, and theengine control unit(ECU) is the most powerful computer on most cars. The ECU usesclosed-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 bestspark timingand determining how long thefuel injectoris open. The ECU does all of this to ensure the lowest emissions and best mileage. SeeHow Fuel Injection Systems Workfor 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 yourPC, 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 1megabyte(MB) ofmemory. 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.