I. Field of the Invention
The present invention relates generally to control systems and, more particularly, to a control system for controlling the exhaust system of an internal combustion engine.
II. Description of Related Art
Modern internal combustion engines include numerous actuators which vary the operation of the internal combustion engine. Such actuators include, for example, exhaust gas recirculation actuators, boost valve actuators and, supplemental fuel injection actuators. The exhaust gas recirculation (EGR) actuator controls the amount of the exhaust gas recirculated to the intake of the engine while the boost control actuator controls the pressure from a turbine at the engine air intake. A throttle control actuator controls the position of the throttle valve while a supplemental fuel injection actuator controls the injection of supplemental fuel either into the engine or into the exhaust system.
The actuation of these various actuators controls various engine operating conditions. Such engine operating conditions include, for example, the exhaust gas temperature and the air/fuel ratio or lambda of the engine.
In order to control the actuation of these engine actuators for optimal engine performance, the previously known systems have associated a PID controller with each of the actuators. These PID controllers, furthermore, operate independently of each other.
Since the variation of one of the actuators, e.g. the exhaust gas recirculation, affects the other engine operating conditions, these previously known control systems have relied upon a microprocessor based engine management unit to control the degree of actuation of the actuators for optimal engine performance. In order to determine the proper amount of actuation for each actuator, the previously known engine management units have relied upon extensive software mapping and software lookup tables to determine the proper amount of actuation for each controller. As such, these previously known engine control systems were necessarily disadvantageously software intensive.