As Corvette has become more technically advanced, this once-elemental sports car has seen a proliferation of onboard actuators installed throughout its body and driveline. Today’s C6, for example, includes a plethora of motor- and solenoid-driven systems to control myriad functions—from the remote-unlocking features on the rear hatch and door locks, to the adjustment of the side-view mirrors, to the various small motors that direct airflow in the HVAC system. Imagine replacing one-third or more of these devices with shape-memory alloys (SMA)—or smart metals, as they are also known—to reduce weight, increase durability, enhance driver convenience, and even improve track-day performance.
That future will become reality on the Corvette as early as later this year, when the next-generation C7 Stingray coupe becomes the first vehicle in GM’s history to utilize shape-memory alloy in lieu of a small-motor-driven actuator system.
“The Corvette is a perfect platform to roll out this material,” says Dr. Paul Alexander of GM’s Vehicle Systems Research Laboratory’s Smart Materials and Research Group. “Chevy’s two-seater has a long track record of introducing cutting-edge material, starting with fiberglass back in 1953, and carbon fiber in the last decade, for example. Whereas those materials are static structural advanced materials, shape-memory alloy is what we call a dynamic advanced material.”
The discovery of shape-memory alloy dates to 1962, when the U.S. Navy’s Naval Ordnance Laboratory observed the properties of nickel titanium (NiTi), and branded it Nitinol. The story goes that the Navy presented a badly bent sample of the alloy at a laboratory management meeting. A technical director wanted to see what would happen if the sample was subjected to heat, so he held his pipe lighter underneath it. To the amazement of those attending the meeting, the sample stretched back to its original shape.
By the late ’90s, OE suppliers had advanced the methods by which SMA ingots were transformed into wire forms. That’s when General Motors became interested in the potential benefits the alloy offered. “Once it was commercially viable for automotive applications, our research-and-development teams started tinkering with it as part of safety research,” Alexander says. “In the past five or six years, smart metals have become a hot topic within our department. [We] set out to prototype SMA systems that could last the 10-year lifespan of a vehicle and perform well across a temperature range of -30 to 85 degrees Celsius [-22 to 185 degrees F].”
Not long after the release of the sixth- generation Corvette Z06 in 2006, the car’s development team came to Alexander with a problem. Specifically, some new Z owners were complaining that pressure built up inside the cabin was making it difficult for them to close the rear hatch.
Alexander explains: “For the base Corvette coupe, GM engineers had implemented a massive cinching latch to address the problem. The hatch drops into the primary latch position, and then a large motor yanks it down, compresses all the seals and struts, and gets it into final latching position. That’s a very bulky mass the team didn’t like, so the mechanism was initially omitted from C6 Z06 models. [It was ultimately added to both the Z06 and the ZR1 for MY2009.]
“Team Corvette asked me to eliminate the parasitic mass of the cinching latch and create a shape-memory-alloy system to remove the excessive cabin pressure. That led me to design a patent-pending SMA actuator in the C6 coupe’s rear fascia called the Active Hatch Vent, or AHV, [which] facilitates the same ease of closing as the cinching latch.”
Shape-memory-alloy wire is very thin—approximately 350 microns in diameter, or about the width of a high E string on an electric guitar—so the mass of a given length of wire is very low. That makes weight savings one of the key features of GM’s new SMA actuators. But that’s just the start of this amazing metal’s benefits.