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Design Innovation Papers

Design and Proof-of-Concept Validation of a Latched Arch Active Seal

[+] Author and Article Information
Monica Toma, Jonathan Luntz, Diann Brei

Mechanical Engineering Department,  University of Michigan, 2350 Hayward Street, 2250 G.G. Brown Building, Ann Arbor, MI 48109-2125

Paul W. Alexander, Alan L. Browne, Nancy L. Johnson

General Motors Research Laboratory, MC 480 106 256, 30500 Mound Road, Warren, MI 48090-9055

J. Mech. Des 134(7), 075001 (Jun 20, 2012) (12 pages) doi:10.1115/1.4006001 History: Received January 23, 2011; Revised November 17, 2011; Published June 20, 2012; Online June 20, 2012

Seals are integral to many industries such as aerospace, marine, oilfield, and automotive. A key performance metric for seal quality is quantified by the normal force between the seal and contact surface. Many applications have conflicting requirements on the normal force depending on the operational state. For example, in panel closures, to ease engagement of the seal the normal force (closing force) should be small; whereas, to maintain a high-quality seal the normal force (sealing force) should be large. While there is an abundance of seal technologies, there still exists a need for adaptable seals that can better accommodate the conflicting demands of multiple operational states and variations in application platforms. This paper introduces an active seal which controls normal force through modification of the structure of a rubber arch seal. While there are several options for actuation, this new technology is modeled, fabricated, and experimentally validated utilizing a shape memory alloy web actuation scheme. Finite element models provide a basis for a parametric study from which design guidelines are derived. The technology and supporting models/processes are demonstrated for an automotive panel closure successfully reducing the closing force by almost 50%, while simultaneously increasing the sealing force by over 30%.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Latched arch schematic architecture. The free end of the main arch is actuated by an SMA web architecture to change the boundary condition of the overall structure. (a) Seal assembly and (b) SMA web architecture.

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Figure 2

Latched arch functioning cycle. The unpowered SMA wire remains cool in the initial door-opened state. The closing of the door compresses the seal with the end of the arch free to slide outward providing a low closing force. Once the door is closed, the SMA is heated to pull the end of the arch inward which latches in place allowing the SMA to be cooled using no power to hold the state of high sealing force. When the door is opened, the free end of the arch passively unlatches returning the seal to its initial state.

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Figure 3

Finite element model representation. The arch is characterized by its radius R, length L, material thickness t, material Young’s modulus E, and the horizontal distance Dh the free end slides outward when the seal is compressed.

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Figure 4

Boundary conditions for the unconstrained arch. In the high sealing force configuration, both ends of the arch are clamped and fixed, while in the closing configuration, one end of the arch is free to rotate and slide outward as the seal is compressed. (a) Sealing configuration and (b) closing configuration.

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Figure 5

Experimental setup for compression measurements. A rubber arch is fixed at one end to a PVC mounting base while the free end slides along the base. A micrometer gauge controls the compression of the arch while a load cell measures the compressive force.

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Figure 6

Unconstrained arch setup. The rubber arch is clamped at its fixed-end and to a moving slider at the sliding (free) end through the use of a compression rod held in place by a series of screws. In the unconstrained state, the sliding end is completely free to slide outward.

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Figure 7

Model validation for unconstrained arch. The compressive force of the arch in both the closing and sealing configurations match well between the FE model and the experiments. The arch produces a sealing to closing force ratio of 1.8 at a full 7 mm of compression.

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Figure 8

Constrained arch prototype. The rubber arch is clamped and fixed at one end while the free end is fixed to a slider. An SMA webbing connects the two ends where the outward sliding of the free end is constrained once the SMA wires become taught. The SMA can be electrically heated to pull the free end inward.

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Figure 9

Model validation over Young’s modulus variation for constrained arch. Sealing and closing force profiles match well between model and experiment for two different materials with different Young’s moduli. (a) Silicone rubber foam and (b) EPDM rubber foam.

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Figure 10

Schematic representation of SMA web actuator. When voltage is applied the SMA wire shrinks and approaches the ends of the web. Li initial width of the web, Lf final width of the web (a) unactuated (martensitic) SMA web and (b) actuated (austenitic) SMA web.

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Figure 11

Young’s modulus impact on sealing/closing force ratio. Model-generated closing and sealing force profiles and sealing to closing force ratio profiles plotted for two different arch material Young’s modulus values demonstrate the independence of force ratio on material stiffness. ( t = 1.6 mm, R = 10.75 mm, Dh  = 3.5 mm, L = 100 mm).

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Figure 12

Sealing/closing force ratio dependence on arch thickness for unconstrained expansion. Model-generated sealing to closing force ratio at full compression plotted over varying arch material thickness are plotted for two different arch radii in the unconstrained arch case show that thin, small radius arches provide the highest force ratio.

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Figure 13

Sealing/closing force ratio dependence on arch thickness for constrained arch. Model-generated force ratio profiles plotted for a variety of arch material thicknesses show that once the free expansion of the arch is becomes constrained, the force ratio is no longer dependent on thickness.

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Figure 14

Sealing/closing force ratio contour map. Contours of constant sealing to closing force ratio at full compression generated from an array of model-based simulations over varying arch radius and allowed-free expansion show that the allowed-free expansion is the primary factor in determining force ratio performance and that the packaging and unconstrained free expansion constraints drive the design to an optimum of largest force ratio.

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Figure 15

Impact of free expansion on seal performance. Model-generated sealing to closing force ratio profiles plotted for different values of allowed-free expansion demonstrated that higher values of force ratio are achieved with larger allowed-free expansions.

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Figure 16

Experimental setup used to measure existing passive seal performance. Case study specification is based on an improvement upon an existing seal whose performance is measured by compressing the seal through a load cell with a digital micrometer to obtain the force-compression profile.

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Figure 17

Latched Arch design prototype for midsize sedan. A rubber arch is fixed to a PVC base at one end and clamped to a slider at the other end. An SMA web actuator is mounted across the two ends underneath the arch. (a) Main arch parameters and (b) single web-cell for SMA actuator.

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Figure 18

Latched arch prototype compression curves. Experimental and model-based sealing and closing force profiles demonstrate that the seal meets the closing specification and well exceeds the sealing specification, as predicted by the design model.

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Figure 19

Full cycle compression measurements. Experimental time traces of the compression distance, compression force, and free expansion distance show that the latched arch prototype provides all the functionality and performance for which it was designed.

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