Digital engine control systems

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Digital engine control systems

            Traditionally, the term powertrain has been thought to include the engine, transmission, differential, and drive axle/wheel assemblies. With the advent of electronic controls, the powertrain also includes the electronic control system (in whatever configuration it has). 

            In addition to engine control functions for emissions regulation, fuel economy, and performance, electronic controls are also used in the automatic transmission to select shifting as a function of operating conditions. Moreover, certain vehicles employ electronically controlled clutches in the differential (transaxle T/A) for traction control.

            These electronic controls for these major powertrain components can either be separate (i.e., one for each component) or an integrated system regulating the powertrain as a unit.

            This latter integrated control system has the benefit of obtaining optimal vehicle performance within the constraints of exhaust emission and fuel economy regulations. Each of the control systems is discussed separately beginning with electronic engine control. 

            Then a brief discussion of integrated powertrain follows. This chapter concludes with a discussion of hybrid vehicle (HV) control systems in which propulsive power comes from an internal combustion engine (ICE) or an electric motor (EM) or a combination of both. The proper balance of power between these two sources is a very complex function of operating conditions and governmental regulations.


Digital engine control

            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 (sometimes more) microprocessor based integrated digital electronic powertrain control. 

            The motivation for the 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.

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