Problems in event based engine control

Physically a four cycle spark ignition engine operates on the basis of four engine processes or events: intake, compression, ignition (or expansion) and exhaust. These events each occupy approximately 180/spl deg/ of crank angle. In conventional engine controllers, it is an accepted practice to sample the engine variables synchronously with these events (or submultiples of them). Such engine controllers are often called event-based systems. Unfortunately the main system noise (or disturbance) is also synchronous with the engine events: the engine pumping fluctuations. Since many electronic engine controllers are event sampled systems, the sampling frequency is thus also frequency locked to the main system disturbances. This creates a signal analysis problem which has, to the authors' knowledge, not been treated in detail in the literature. This paper concerns itself with the impact of this and related problems on accurate air/fuel ratio control of a spark ignition (SI) engine.