Discrete-Event IC Engine Models: Why the Constant Speed Assumption is Valid
Lino Guzzella · Journal of Dynamic Systems Measurement and Control · 2003
Internal combustion (IC) engine models are often formulated as discrete-event models. This formulation captures well the reciprocating behavior of the engine and often leads to simpler system equations. The independent variable of these models is the engine’s crank angle which, because in general the engine’s speed is not constant, is not increasing linearly with time. Nevertheless, it is standard practice in industry and academia to apply discrete-time control system analysis and synthesis tools to these systems. Of course, this approach is justifiable only if the engine speed is varying very slowly compared to the other dynamic effects. In this paper it will be shown that this assumption is indeed valid in most cases, i.e., that for typical engine systems the speed dynamics are at least one order of magnitude slower than the manifold dynamics.