Modal Transient FEA Study to Simulate Exhaust System Road Load Test 2011-01-0027

Durability life is one of the major concerns in the automotive industry. Road Load Data Acquisition (RLDA) is one of the most important steps to verify exhaust system durability performance. RLDA will not only provide data for system level rig testing drive file development but also for exhaust components validation (computing safety factors). Modal transient FEA can be utilized to simulate either vehicle durability testing or sub-system level rig testing. How to simulate correctly is critical in the simulation. One of the most challenging portions in the full exhaust system simulation is isolator modeling due to its non-linear characteristics. However, we have to use linear modeling to simulate isolator in modal transient analysis, which induces errors. As FEA analysts and engineers try to eliminate isolators in the full exhaust system analysis to achieve more accurate analysis results, some has proposed to directly exert excitation (displacement or acceleration) on exhaust side hangers.

In this paper, several studies are performed to address this question. First, a two degree of freedom (2 DOF) system is analyzed; second, 2D and 3D beams are studied. Last, FEA comparison between body side input and exhaust side input are conducted for an exhaust system. The theoretical analysis shows that the changing input location and modifying boundary conditions accordingly, the analysis results are consistent. However, for modal transient analysis, input directly from exhaust side hangers will result more errors. Observed is more inaccuracy for the stress than displacement results, and the analysis results are reasonable if inputs are from body side. The study demonstrates that the errors are from both input error and numerical error, and input error on exhaust side will impact analysis results significantly. However, input error on body side is not much sensitive on analysis results. Therefore, inputs from body side are recommended in exhaust system modal transient simulation and inputs from exhaust side will not be utilized to have more reasonable and accurate simulation results.