In fact, most modern engine control systems, s are digital. A typical engine control system incorporates a microprocessor and is essentially a special-purpose computer (or microcontroller).
Electronic engine control has evolved from a relatively rudimentary fuel control system employing discrete analog components to the highly precise fuel and ignition control through 32-bit (sometimesmore) microprocessorbased integrated digital electronic powertrain control. The motivation for development of the more sophisticated digital control systems has been the increasingly stringent exhaust emission and fuel economy regulations. It has proven to be cost effective to implement the powertrain controller as a multimode computer-based system to satisfy these requirements.
A multimode controller operates in one of many possible modes, and, among other tasks, changes the various calibration parameters as operating conditions change in order to optimize performance. To implement multimode control in analog electronics it would be necessary to change hardware parameters (for example, via switching systems) to accommodate various operating conditions. In a computer-based controller, however, the control law and system parameters are changed via program (i.e., software) control. The hardware remains fixed but the software is reconfigured in accordance with operating conditions as determined by sensor measurements and switch inputs to the controller.
The primary purpose of the electronic engine control system is to regulate the mixture (i.e., air–fuel), the ignition timing, and EGR. Virtually all major manufacturers of cars sold in the United States (both foreign and domestic) use the three-way catalyst for meeting exhaust emission constraints. For such cars, the air/fuel ratio is held as closely as possible to the stoichiometric value of about 14.7 for as much of the time as possible. Ignition timing and EGR are controlled separately to optimize performance and fuel economy.
the engine control system is a microcontroller, typically implemented with a specially designed microprocessor and operating under program control. Typically, the controller incorporates hardware multiply and ROM. The hardware multiply greatly speeds up the multiplication operation required at several stages of engine control relative to software multiplication routines, which are generally cumbersome and slow. The associated ROM contains the program for each mode as well as calibration parameters and lookup tables. The earliest such systems incorporated 8-bit microprocessors,
although the trend is toward implementation with 32-bit microprocessors. The microcontroller under program control generates output electrical signals to operate the fuel injectors so as to maintain the desired mixture and ignition to optimize performance. The correct mixture is obtained by regulating the quantity of fuel delivered into each cylinder