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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), vehicle lift and downforce, and cooling/heat exchange for the vehicle powertrain and A/C systems. While active devices are present on all aircraft, the majority of known airflow control devices in current use in ground transportation are of fixed geometry, location, orientation, and stiffness. The project, conducted during the 2004–2006 timeframe, whose performance requirements, design, and bench-top prototype build phases, are described in this paper was successful in developing an SMA actuator based approach for opening and closing a vertically-oriented-blade louver system to be used for on-demand control of the airflow into the engine compartment, i.e. for on-demand control of both cooling airflow as well as aerodynamic drag. Beyond feasibility, the initial full scale bench top working models demonstrated an active materials based approach which would have decreased weight and a smaller packaging envelop than a comparable motor driven unit. This demonstration showed that actuation speed, force, and cyclic stability all could meet the application requirements. The specific design that was selected, a set of parallel vertically oriented blades each linked through a gear to a common rack that is translated by a linear SMA actuator, uses straight linear actuation to produce a reversible synchronous 90 degree rotation of the blades, i.e. a full opening and closing capability for the louver system. Key technical issues that remained to be demonstrated and resolved through design modifications if necessary in Part 2 — on-vehicle performance testing — of this study were related in most part to robustness in the harsh vehicle front-end environment, a prime example being mechanism stalling due to ice or mud buildup.Copyright © 2013 by ASME and General Motors |
