Modeling and Realtime Simulation of an Automatic Gearbox using Modelica

To speed up the development cycle of electronically controlled mechanical devices, hardware-in-the-loop simulation is used more and more. Applying this method to an automatic gearbox of a car, the electronic transmission control hardware is tested against a model of the gearbox, which is simulated in realtime. Modeling such a system is a demanding task, because its structure varies during gearshift. Since the gearbox investigated has six switching elements (clutches and freewheels) the actual structure has to be found amongst 2^6=64 possible configurations. It is shown how such a variable structure system can be modeled with Modelica and how a consistent configuration can be found in realtime after a gearshift occured. The results presented show that it is possible to simulate variable structure systems in realtime using standard realtime simulation hardware and appropriate software tools