SI Engine Controls and Mean Value Engine Modelling

Many existing classical electronic control systems (speed-throttle, speed-density, MAF (mass air flow)) are based on quasistatic engine models and static measured engine maps. They are thus time consuming to adapt to new engine types, are sensitive to dynamic sensor errors and in general have undesirable dynamic characteristics. One of the main reasons for the characteristics of these strategies has been the lack of a precise, systems oriented, equation based, dynamic engine model. Recently a compact dynamic mean value engine model (MVEM) has been presented by the authors which displays good global accuracy. A mean value model is one which predicts the mean value of the gross internal and external engine variables. This paper shows how the engine model can be applied to the systematic design and analysis of classical electronic engine control systems.

One of the main aims of the paper is to eliminate the use of cut and try methods in designing dynamic engine controls. The goal is also to improve transient drivability and emissions performance. The main subjects treated are steady state and transient fueling strategies, lambda control and idle-speed control. There is also a comparison of conventional speed density and MAF control systems including the limitations imposed by signal conditioning filters and available sensors.