Structural Dynamics Characterization of the Vehicle Seat for NVH Performance Analysis

Most of the researches about the transmission of the vibration to the vehicle seat had little or no focus on the structural modal characteristics of the seat while these characteristics can have large effects on the transmission of the vibration to the vehicle occupant. To realize these structural effects the main modal characteristics of a front seat of sedan car haven been characterized by performing modal tests. The experimental results showed that seat has some major mode shapes at frequencies below 80 Hz. Among these major modes, the seat torsion mode was focused as its resonance frequency was near the selected car body torsion mode. The interaction of this seat mode with the car body, here BIW (body-in-white), torsion mode was evident by a large seat vibration level in the frequency response of the seat to the front main member of the car BIW. To reduce this interaction, the seat structure needs to be considerably changed. However, such changes are only possible in the early design phase. To predict and optimize the seat structural dynamics, in early design phase where there is no enough detailed design data, CAE beam concept models for BIW and the seat were developed. The developed BIW beam model was consisted of the following main members of the engine compartment, the floor members, body side members, roof members, as well as the trunk members. For development of seat CAE concept beam model we have used similar approach as it was used for above mentioned BIW. CAE NVH analyses of the concept beam model of the body and seat (BIW+ front seat) have shown similar results with the corresponding advanced CAE model results. The concept CAE model results similarly indicate that if the seat resonance frequency and the body resonance frequency are close, it may become a cause of large seat vibration. It is shown that these beam concept models can be used to predict and optimize the seat vibration. The proposed method can be used as an important tool to improve the NVH performance of the seat vibration in early design phase.