Important Modeling Practices in CAE Simulation for Vehicle Pitch and Drop 2006-01-0124

Vehicle pitch and drop has become an important subject to crash analysis due to the recent FMVSS208 requirements for unbelted occupant. During frontal impact, the excessive header drop due to significant vehicle pitch and drop can induce the contact between occupant's head and sun visor. To avoid this issue, structure design for reducing vehicle pitch and drop is essential to crash safety. Historically, CAE simulation has been used in structure design during vehicle development process. Therefore, the quality of CAE modeling for replicating vehicle pitch and drop at physical test is crucial for assisting the structure design. In this paper, the most effective components in CAE model to vehicle pitch and drop have been identified and ranked by using the results of the sensitivity study. Hence the model quality can be emphasized on those major components including front horn, kick-down of front frame, body structure at upper load path, and body mounts. In addition to the sensitivity study, other important factors affecting the accuracy of CAE simulation for pitch and drop are also discussed. These factors are the mass distribution, gravity, tire, and suspension modeling. Due to the gravity effect, the suspension and structure components in test vehicle are compressed and initially remain at equilibrium state. This is different than the CAE simulation where it usually starts without pre-loaded structure. To compensate the discrepancy of initial conditions between CAE and actual test, a simplified subtraction method is suggested. The CAE results with suggested modeling practices demonstrate reasonable correlations to the test data.