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Proceedings Paper

Feasibility study of the dual-chamber SMART (SMA ReseTtable) lift device
Author(s): Jonathan E. Luntz; Diann Brei; Joe Ypma; Jonathan R. Young; Joshua Radice; Nancy L. Johnson; Alan L. Browne; Kenneth A. Strom
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Paper Abstract

Pedestrian protection is a major focus of automotive crashworthiness with new regulations taking effect worldwide. While there are many approaches to reducing the head-injury-criteria (HIC), a leading approach is to actively lift the hood to increase the crush distance to rigid underhood components. Most current lift devices are single-use, requiring the hood to be manually returned to a drivable position, and may damage the hood during lift due to inappropriate lift rates. This paper addresses these issues with an alternative approach using stored energy marrying conventional (pneumatic) and smart materials (Shape Memory Alloy) actuation. The SMART (SMA ReseTtable) hood lift device comprises a dual chamber cylinder which releases stored pneumatic energy via an ultra-fast SMA exhaust valve, raising a piston attached to the hood. The device can be automatically reset and rearmed through pressurization of the chambers and the energy dissipated for service by evacuating both chambers. This approach is unique in that several design parameters such as pressure and valve opening/timing profile can be altered in the field to compensate for temperature, added mass (such as snow) or platform changes. This paper presents the concept of this device and the parametric design of the pneumatic cylinder and valve orifice based on an analytical performance model. Two valve concepts are presented: direct and indirect, where the direct valve is simpler and more controllable, but the indirect valve can provide larger orifices (and therefore faster lift times) with reduced actuation requirements. Using a combination of analytical model-based and experimental methods, the SMART lift device with each valve approach was designed, and a full-scale prototype built and experimentally characterized validating the model and successfully demonstrating feasibility of each system to meet and exceed the pedestrian protection specifications. This new set of technologies enables the hood lift application with added functionality such as tailorability and resettability.

Paper Details

Date Published: 11 April 2007
PDF: 15 pages
Proc. SPIE 6527, Industrial and Commercial Applications of Smart Structures Technologies 2007, 65270V (11 April 2007); doi: 10.1117/12.715727
Show Author Affiliations
Jonathan E. Luntz, Univ. of Michigan (United States)
Diann Brei, Univ. of Michigan (United States)
Joe Ypma, Univ. of Michigan (United States)
Jonathan R. Young, Univ. of Michigan (United States)
Joshua Radice, Univ. of Michigan (United States)
Nancy L. Johnson, General Motors Corp. (United States)
Alan L. Browne, General Motors Corp. (United States)
Kenneth A. Strom, General Motors Corp. (United States)

Published in SPIE Proceedings Vol. 6527:
Industrial and Commercial Applications of Smart Structures Technologies 2007
L. Porter Davis; B. K. Henderson; M. Brett McMickell, Editor(s)

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