Improvement of CAE Prediction Quality of NVH Full Vehicle Models by Applying Hybrid Methods

摘要

Calculations with a NVH full vehicle model are in principle possible for vibrations and low-frequency acoustics. In the mid-frequency and kHz range other models with different CAE methods need to be applied. To design dynamic and structural behavior of vehicle components, either MBS or FEM models are used which contain only the components, in free-free or grounded state. The components may be included in a full vehicle model to assess and optimize them in a more realistic vibration environment. As the development process progresses, the pre-designed components and their interplay in the vehicle will be examined for relevant operating modes. The simulation becomes more complex and the challenges for CAE increase. A classical full vehicle model consists of a trimmed body, interior air cavity, powertrain, and chassis. Depending on the complexity of the engineering tasks, different large models and simulation methods are applied in the Mercedes-Benz Cars Development, each with specific advantages and drawbacks. Besides the MBS and FEM methods additionally there are hybrid methods: - MBS in which the flex-body modes of relevant FE models are embedded in the MBS model. - To avoid deficiency in the modeling, FE calculations are performed to assess the chassis and powertrain NVH quality in which the body is represented by test data. - Hybrid methods coupling digital simulation with prototype testing results (via a self-developed engineering tool) are used to solve complicated systems where CAE is inadequate in predicting the powertrain noise. In the design of a new car, booming noise, droning, tyre cavity resonance are well-known NVH phenomena that present significant challenges. The way they can be treated by simulation will be shown with an example using the coupling of FEM with test data.