Concept Level Cross Car Beam NVH Simulations

Abstract

The Cross-Car Beam (CCB), which is located below the Instrument Panel, supports the steering column, dashboard and the passenger air bag. Designing the CCB is crucial for architecture development and it is a part of the platform definition process. It plays a major role in meeting the NVH targets for the vehicle. Alternate materials have been tried out to reduce weight of the Cross-car beam assembly, but cost of the assembly goes up. Another option is to opt for material thickness reduction of the CCB or the steering column bracket which will reduce weight but that will have an impact on the structural mode and natural frequencies. The NVH performance mustn’t drop below the program NVH targets after weight reduction. The goal of this paper is to define the geometry and the sections of the CCB & Steering assembly by reducing weight without compromising NVH performance and meeting architectural inputs in the concept stage of the project. While the preliminary architecture is being developed, the relevant inputs and NVH targets will be taken as inputs for the study. A concept simulation model is set-up which is capable of quick simulations. A design optimization will be performed based on the model and the optimized CCB concepts will be taken forward for detailed engineering later. The CCB assembly has been parameterized into 23 parameters which include the geometry, sections & architectural parameters. This complete assembly has been modelled as beam elements and the joints have been considered as rigid joints and the constrains were applied. Modal analysis was performed to obtain the natural frequencies. A Design of Experiments (DOE) was run on these parameters to identify the critical parameters with respect to the weight and natural frequencies. The DOE gives a mathematical model for optimization and the sensitivity and direction of goodness of all the parameters. The mathematical model generated is used to perform design optimization. Based on the optimization, 10% weight reduction was achieved in the CCB assembly with optimal geometry and sections. The results match closely with the CAE results obtained after detailed CAD is analysed. This simplified beam model of the assembly takes less than 5 minutes to run and the iterations can be automated within the software. This makes it possible to run multiple DOEs and study different solutions. It is even possible to analyse various alternatives proposed. The process of defining the architecture is fastened as the optimization of the CCB can be carried out within a few days.