Experten-Forum Powertrain: Simulation und Test 2019 by Johannes Liebl

Author:Johannes Liebl
Language: deu
Format: epub
ISBN: 9783658287078
Publisher: Springer Fachmedien Wiesbaden

1 Introduction

The goal of this paper is to give the reader an introduction into the possibilities of combining a detailed and flexible MBD model of an ICE, with a testbed set-up, a detailed DMF and an online load generation with automation system models to analyze the engine design for varying loading conditions under any user specified (true) transient speed-load profile.

Simulations are already widely used in engine and power unit component development as well as in trouble shooting. In addition to structural and flow simulations, multi-body dynamics (MBD) is taking on an ever more important role in providing realistic boundary conditions for nonlinear component lifetime analyses [12] as well as providing, e.g., advanced elasto-hydrodynamic (EHD) bearing simulation results. Such MBD model is typically in 3D – in sense of covering coupled bending and torsional vibrations – and making use of flexible (typically FE-based) structures. Multi-body simulations are typically performed for quasi-stationary conditions, for few engine cycles within a speed sweep or for non-stationary conditions without heavy transient effects such as a slow engine run-up [1]. The system analyzed is a purely mechanical one. Cylinder pressure loads are simplified by applying predefined loads. This is suitable for steady-state conditions, but insufficient to cover non-stationary transient effects. Workarounds for analyzing the transient phenomena with predefined (gas) forces and torques within a certain load transient often lead to speed instabilities during transients and require manual iteration on adjusting the load and speed boundary conditions (BCs), often with less than satisfactory capturing of the transient phenomena.

Another important simulation approach uses pure torsional models, solved in frequency or time domain [9]. Both are much faster than the 3D MBD one and the transient approach also enables the investigation in non-stationary effects during longer duration of multiple seconds real time instead of only few engine cycles [2]. Also, for such models, typically predefined loads are used whereas for extended approaches, controlled torque is applied. A disadvantage is that mainly general torsional dynamics can be investigated, but not the coupled bending effects and detailed investigations in structural durability or bearings in the same model.

Isolation elements are mostly set-up as separate (rigid) MBD model (detailed and physical model) and derivate or map-based models are extracted and used within the two previously discussed approaches or in best case the detailed model is integrated in the torsional model. [3] presents different modeling levels of driveline and DMF.

System boundary conditions are also important for the component behavior as its loading can be different. It is easy to understand, that torsional system is different between vehicle installation or on a testbed without transmission and different drive shafts. However, very often such installation also leads to significant different bending behavior. The latter is most likely caused by different flywheel bending – or even breaking – due to an artificial flywheel (e.g. same total inertia to adjust the torsional set-up, but different mass and center of gravity) on a testbed and different radial support. If problems on a testbed with such different and wrong BCs

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