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Airflow over/under/around a vehicle can affect many important aspects of vehicle performance including vehicle drag (and through this vehicle fuel economy) and cooling/heat exchange for the vehicle powertrain and A/C systems. The vast majority of known devices in current use to control airflow over/under/around the vehicle are of fixed geometry, location, orientation, and stiffness. The project whose performance requirements, design, and build phases are described in this paper was successful in developing an SMA actuator based approach to the on-demand reversible deployment of an air dam through vertical translation. Beyond feasibility, the initial bench top working models demonstrated an active materials based approach which would add little weight to the existing stationary system, and could potentially perform well in the harsh under vehicle environment due to a lack of exposed bearings and pivots. This demonstration showed that actuation speed, force, and cyclic stability all could meet the application requirements. The solution, a dual point balanced actuation approach based on shape memory alloy wires, uses straight linear actuation to produce a reversible height change of 50 mm. Key technical issues with regard to design remaining to be resolved given the harsh under vehicle environment are in most part related to improved system robustness, a prime example being mechanism sealing. |
