Engine Control Units

Engine Control Units

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. Gathering data from dozens of different sensors, the ECU knows everything from the coolant temperature to the amount of oxygen in the exhaust. more :

With this data, it performs millions of calculations each second. The Engine Control Unit also performs operations 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. 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. In order to provide the correct amount of fuel for every operating condition, the engine control unit (ECU) has to monitor a huge number of input sensors. Mass airflow sensor - Tells the ECU the mass of air entering the engine
Oxygen sensor(s) - Monitors the amount of oxygen in the exhaust so the ECU can determine how rich or lean the fuel mixture is and make adjustments accordingly
Throttle position sensor - Monitors the throttle valve position (which determines how much air goes into the engine) so the ECU can respond quickly to changes, increasing or decreasing the fuel rate as necessary
Coolant temperature sensor - Allows the ECU to determine when the engine has reached its proper operating temperature
Voltage sensor - Monitors the system voltage in the car so the ECU can raise the idle speed if voltage is dropping (which would indicate a high electrical load)
Manifold absolute pressure sensor - Monitors the pressure of the air in the intake manifold
The amount of air being drawn into the engine is a good indication of how much power it is producing; and the more air that goes into the engine, the lower the manifold pressure, so this reading is used to gauge how much power is being produced.
Engine speed sensor - Monitors engine speed, which is one of the factors used to calculate the pulse width