“Since the wires are so thin, we can make very-low-profile actuator packages, which conform or ride along surfaces of existing components. In comparison, we look at a small motor as an extra brick of material that has to be packaged in. We can put SMA actuation in locations where a conventional motor or solenoid is too large.
“SMA actuator systems use solid-state technology, and that makes them more reliable than traditional actuators, which are composed of rotors, stators, brushes, windings, and bearing surfaces.
“SMA [also] produces a very quiet operation. Unlike a motor- or solenoid-driven actuator, which can annoy a Corvette owner with a lot of whirring and clunking, an SMA actuator produces an audibly quiet motion without external noise generation. More so, it’s completely electromechanically quiet. In other words, there is no signal interference of the kind a conventional motor produces. That means we can put this technology next to antennas, which is exactly what we did on the 2014 Stingray.”
So is shape-memory alloy simply a fad, or does it signal the future of automotive-actuator technology?
“I definitely think it’s the future.” Alexander says. “There’s a large number of opportunities where shape-memory-alloy actuation really does make sense. One of our jobs now is to educate the supply base and the designers within GM, so that they’re comfortable employing it.
“As far as the C7 Corvette goes, the vehicle is definitely blazing a trail here with SMA technology. I’m confident this Active Hatch Vent application will be successful, and I hope you’ll see some of the projects we’re working on [for Corvette] come to fruition a little bit quicker. Looking out further, I think shape-memory-alloy actuators will proliferate across all sorts of applications—both on-demand triggered applications and passively actuated applications where SMA is both a sensor and an actuator. I think SMA’s successes will start adding up very quickly.
“This is the initial rollout of this device, so it’s specifically tied to rear-hatch opening and closing,” Alexander reiterates. “But as you can imagine, almost anywhere that small-motors and solenoids are currently utilized on the Corvette, shape-memory alloys can potentially take their place.”
How the C7’s Active Hatch Vent (AHV) Works
1. A Corvette owner opens the rear hatch.
2. The action triggers the “ajar” sensor in the hatch latch.
3. The Corvette’s body control module (BCM) receives this input and enables the Active Hatch Vent (AHV).
4. The vent’s onboard controller receives the enable signal and begins sending power (Pulse Width Modulated [PWM] 12-volt/1.0-amp) to the wire to heat it.
5. As the wire transforms, it contracts and opens the vent within about four seconds of the enable signal being sent to the actuator.
6. Once the vent is open, it stays open as long as the hatch is ajar. At this point, the onboard controller has regulated the power to maintain the target opening angle for the vent, trickling just enough current through the wire to keep it above its transition temperature (around 300 milliamps).
7. When the rear hatch is shut, the pressurized air rushes out of the cabin through the open vent to allow for easy closing. GM’s in-vehicle testing has shown a 25 to 30 percent reduction in required input closing energy.
8. Once the latch sensor reads “closed,” the BCM shuts off the enable signal, and the onboard controller shuts off power to the SMA wire.
9. The wire cools naturally and transforms to its more malleable state. A bias spring within the device then stretches the wire to its initial length and seals the vanes of the vent against its housing. This sealing step takes less than a second in most ambient conditions.