As automobile use expands in population-dense cities across the world, there is a growing need for new approaches to mitigate the consequences to pedestrians of pedestrian/automotive collisions. This is especially challenging for passive approaches since there is an increasing internal space demand that reduces the crush zone between the relatively compliant hood and rigid underhood components. One unique approach is an active hood lift which raises the hood upon detection of a collision with a pedestrian to increase the crush zone. This approach is technically challenging due to the fast and accurate timing which is sensitive to extrinsic factors (including pedestrian height and weight and the need for reusable/automatically resettable functionality. This paper presents a novel hood lift concept: the shape memory alloy ReseTtable (SMArt) dual chamber lift device which is reusable, automatically resettable, and has tunable performance both off-line, and on-line to adjust to extrinsic factors. This device is situated under the rear corners of the hood and stores energy in the form of compressed air in opposing sides of a dual chamber pneumatic cylinder and a high-speed shape memory alloy exhaust valve (SEV) vents the upper chamber within milliseconds to allow the lower chamber to deploy the hood. A general multistage sequential design process is outlined that enables lift timing performance to be tailored by parametric design off-line and by varying operating parameters on-line. A proof-of-concept prototype was built and experimentally characterized for a midsize sedan case study confirming the timing, load capability and stroke of the device on the benchtop and the complete operational cycle in a full-scale automobile hood bay. The impact of additional mass on the lift timing was measured and two on-line adjustable operating parameters (pressure and valve timing) were investigated for their ability to compensate for the mass and other extrinsic effects. While this was a limited study of this new active technological approach to pedestrian safety, it does indicate promise to meet the strict demands of an active lift and a tailorable, resettable/reusable device.

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