Virtual Testing Approach of a V6 Engine with Detailed DMF Under High Dynamic Transient Speed-Load Profiles (Virtueller Testansatz eines V6-Motors mit detailliertem ZMS unter hochdynamischen, transienten Lastprofilen)

Structural dynamic simulation is used for virtual testing of engines and powertrains following different approaches, based on target application, development process phase or during troubleshooting. Basically, we can distinguish the pure torsional and transient multi-body approaches (MBD), rigid or flexible structures and the level of detailing.

Another important aspect is the type of operating conditions. Typically, different operating conditions under constant speed and load are analyzed in frequency domain or during a quasi-stationary transient. The current trend of electrification leads to a reduction in base engine development, but with the necessity for more detailed improvements of existing engines and going closer to the limits of materials. Furthermore, we face a growing development of hybrid drives. Both demand an increase in accurate prediction of dynamics in crank train and entire driveline under more complex operating conditions close to reality, where the engine is often the subject of highly fluctuating loading conditions and anomalous phenomena by controls, irregular firing, or auxiliary units. In particular, the transition between operating conditions like the run-up, or ICE start-stop and effects from highly transient operating conditions should be investigated to ensure a robust operation and to avoid failures, due to their change of torque flow and activation/deactivation of components. A clear benefit of virtual testing of such transient loading conditions is the easy adaptability of the simulation even at difficult-to-test loading conditions, at very little cost.

Another important cornerstone is the correct consideration of complex driveline (isolation) elements, such as a dual mass flywheel (DMF), clutch, torque converter or pendulum absorber damper. Those have due to their highly non-linear characteristic a strong influence on the entire dynamics, especially under non-stationary conditions. Therefore, detailed (in best case physical) models need to be implemented in the entire model.

This generates the need to combine detailed flexible MBD models, considering coupled bending and torsional vibrations, with detailed driveline elements like a DMF and to operate under non-stationary operating conditions in a controlled way. In this document, the authors describe how to build such models, in order to achieve a true transient MBD analysis with any user specified speed/load profile to investigate in vibrations, durability and comfort related issues in the power unit.

This requires a few essential functionalities like a cylinder pressure generator, for each cylinder with the cylinder forces and resistive torque, engine automation system to control speed/load, given as an input to the multibody model, and interfacing of the flexible MBD model with a detailed physical model of DMF.

As a demonstration, a multibody model of a V6 engine is described, installed on a testbed with its driveline and dyno, including a model of the DMF and coupled to an automation model for controlling the firing pressure. With such a setup, it can be demonstrated how the engine responds to a transient speed-load change, in a form of misfire or start-stop.