<p>In recent years, active structures are being developed for implementation in vehicles of the future. One part of vehicle that is ripe for innovation is a car seat. Plenty of research has been conducted in modifying car seats to make them more responsive to the occupant’s motion, especially for the new generation of semi-autonomous cars. One such area of active research is responsive seat bolsters that respond to the occupant motion during tight turns and hard corners. Many of these active seat bolsters have been implemented using pneumatic systems. However, these systems add additional weight and complexity to the vehicle. Due to the recent trend in increased electrification of the vehicles, actuation systems that use direct electrical power seems more natural. Recently, many of these active structures have been made from advance actuators such as shape memory alloys (SMA). These SMA actuators have tremendous advantages over conventional actuators, in terms of specific power and work density.</p><p>A new active seat bolster design using lightweight SMA wires will be presented. The bolster consists of two thin curved polymer sheets connected using cylindrical hinges. These hinges perform multiple functions; as a support structure for SMA wires and for electrical connections. When the seat is occupied, the seat bolster absorbs this dead load by bending of the curved plates and stressing the SMA wires. Using finite element method, simulations are conducted to ensure that these stresses in the unactuated state are under the material limits and the tensile strain in SMA wires are small enough so that the required bolster actuation displacement is achieved. The structural model of the bolster is developed from two-dimensional scans of the curved polymer sheets. The structural model response is calibrated using experimental force displacement response of the hinged curved polymer sheets without SMA wires. Applying the experimental tensile stress-strain curve of the SMA wires, the unactuated strain in the wires is determined from the calibrated numerical model. Experiments are then conducted on the bolster with SMA wires, and the force-displacement actuation response of the structure is measured using constant displacement loading. In the experiments, the SMA wires are heated by means of joule heating and cooled by natural convection. The numerical simulation is carried out in multiple steps to ensure the correct stress state in the structure before the SMA actuation. The actuation response of the numerical model is validated with experiments on the active bolster structure. The presentation will focus on the design, experiments, and simulation of SMA wires actuated seat bolster.</p>

On Active Seat Bolsters Using Shape Memory Wires

Paper Proceedings: https://asmedigitalcollection.asme.org/SMASIS/SMASIS2021/volume/85499

ASME 2021 Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS2021)

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