You might not often think about them, but the springs in your car’s suspension are a key piece of technology—and one that has been largely unchanged for decades. The simple steel coil spring has served in effective anonymity—but its days may be numbered. Audi is planning to put a lightweight composite spring into production by fall 2014.
The glass fiber-reinforced polymer, or GFRP, springs will save about 40 percent of the weight of steel springs, cutting about 2.5 pounds per spring for a larger mid-size car. That amounts to a savings of 9.7 pounds total, half of which is unsprung mass.
Unsprung mass relates directly to a car’s handling and ride quality, and reducing it can yield even larger dividends than a similar weight reduction from the car’s sprung mass (i.e., from the car’s body). Ford has shown a lightweight concept car using similar composite spring technology, but hasn't announced any plans for production.
“The GFRP springs save weight at a crucial location in the chassis system. We are therefore making driving more precise and enhancing vibrational comfort,” said Dr. Ulrich Hackenberg, Member of the Board of Management for Technical Development at AUDI AG.
But how durable are these GFRP springs? Can they take the same stresses as steel? Audi thinks they can. In addition to being larger in overall diameter and sporting a smaller number of coils, the GFRP springs are composed of long glass fibers twisted together then impregnated with epoxy resin. This glass-resin structure is then wrapped with more glass fibers at counter-poised 45-degree angles. The multi-ply structure is designed to support and absorb the stresses the spring undergoes during driving. Once formed, the spring is cured at more than 100 degrees Celsius (212 degrees Fahrenheit).
The GFRP springs are composed of resin and glass fiber, and therefore cannot corrode, and is impervious to a wide range of chemicals, including harsh wheel cleaners. Audi also notes that the production process consumes far less energy than the production of steel coil springs.