Occupant Vibrations - A Challenge for Seat Development 2016-01-1432

Predicting the vibration comfort is a difficult challenge in seat design. There is a broad range of requirements as the load cases strongly vary, representing different excitation levels, e.g. cobblestones or California roads. Another demand is the driver expectation, which is different for a pickup and a sports car. There are several approaches for assessing the vibrations of occupants while driving. One approach is the evaluation of comfort by integral quantities like the SEAT value, taking into account a weighting based on the human body sensitivity. Another approach is the dimension of perception developed by BMW, which is similar to psychoacoustics as the frequency range is separated with respect to occurring vibration phenomena.

The seat transmissibility is in the focus of all activities. In the frequency range it defines the relation between the input at the seat slides and the output at the interface of human body and trim. The seat transmissibility represents only the occupied seat behavior, describing the reduction or decrease of vibrations applied on the seat slide. For its computation, the interaction of all model parts, i.e. the human body, the foam pads and the seat structure have to be considered. Simplified setups, such as using a rigid mass as an occupant, enable only evaluations with limited information to optimize the dynamic seating comfort.

The paper shows the theory behind seat dynamics, describe the influence of the main parts, i.e. occupant, foam and structure, on the seat transmissibility and will finally give an overview on current approaches for the assessment.