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ZF eyes structural applications

By: Rhoda Miel

January 24, 2013

DETROIT — German automotive supplier ZF Friedrichhafen AG is known as a transmission specialist and a chassis supplier, with lots and lots of metals-intensive parts.

But the push for lower weight and improved fuel performance is changing that, and the company is increasingly investigating reinforced plastics for structural applications.

"Lightweighting is very important for us," CEO Stefan Summer said during a Jan. 15 press conference at the North American International Auto Show in Detroit. "We are developing not only new designs, but new materials like fiberglass materials and carbon materials."

In fact, plastics is not a completely new material for ZF. It already is producing brake pedal systems made of glass-reinforced thermoplastics, said Dieter Eulenbach, director of sales and engineering for ZF's suspension group in North America, based in Northville, Mich.

Brake pedals were the last pedal system to go to plastics, out of concerns about the pressure placed on them during emergency situations, but Eulenbach said they are only the beginning of what ZF is considering in both thermoset and thermoplastic composites.

One prototype under development at ZF is a long-glass-fiber-reinforced, transverse leaf spring within an axle system. The flexibility inherent within the plastics in the composite leaf spring would eliminate the need for metal coil springs, reducing complexity within the axle while also cutting weight by 12-15 percent, he said.

ZF said the plastic brake pedal system is half the weight of a steel system.

The axle is targeted for future large-volume vehicles.

ZF also is developing a lightweight suspension strut wheel carrier that would use a hybrid mix of materials, including plastics, which would be half the weight of a traditional steel and aluminum strut.

The system would place an all-plastic suspension part at the top of the wheel carrier and encase a steel piston rod within plastic on the lower half.

The finished part would consist of one part sent to automakers, rather than three, which reduces assembly time and costs as well.

"[Plastics] offers you a lot of interesting perspectives in your parts," Eulenbach said.

At this point, ZF is focused more on near production using glass-fiber reinforcement rather than carbon fiber, simply because the industry already has decades of studies available on how glass reinforcement will act in real-world conditions.

"We need to look at 10 years' worth of data, and that's simply not there yet for carbon," he said, although increased use of carbon fiber in the auto industry is making that information available quickly.