Structural dynamics of the automotive body: Effects of rear overhang on ride comfort

Most of the researches about vehicle ride comfort and effects of the car body vibration on vehicle occupant had little or no focus on the structural modal characteristics of the vehicle body while these characteristics can have large effects on the transmission of the vibration to the vehicle occupant. One of the issues of the automotive ride comfort is related to the transmission of the vibration from the rear suspension to the rear seat mounting and therefore the seat and the vehicle occupant. Since such vibration are mainly caused by the rear body structure torsion mode, more care is required to predict the characteristics of this torsion mode in early design phase of the car. When the predecessor platform is resized for using a new car, it is sometimes necessary to extend the rear overhangs of the car. This research shows that the length of rear overhang may have a large effect on the torsion mode of the body and therefore on the transmission of the vibration from the road or rear suspension (shock absorbers) to the rear seat mountings. When a same platform is used for two similar models with different lengths of rear overhangs, the rear seat vibration level can considerably be different for these two similar models. An automotive CAE concept beam model, here, is used to investigate the effects of rear overhang on the rear seat vibration and comfort level. CAE beam concept models for the car body are important tools are used to predict and optimize the structural dynamics, in early design phase where there is no enough detailed design data.