Composites take prime chassis roles at ZF

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Composites take prime chassis roles at ZF

The ZF rear axle study with wheel-controlling transverse composite leaf spring (shown in green) depicts functional integration and lightweight construction in a passenger-car chassis.

A transverse axle layout and a strut module with integrated wheel carrier are design proposals from ZF that spotlight weight reduction by putting an accent on composite usage.

The lightweight axle design features a transverse leaf spring—made of epoxy resin and continuous-glass-fiber filaments—to handle rear suspension and stabilizing functions as well as rear wheel guidance.

ZF says its rear suspension with composite leaf spring is approximately 12% lighter than a conventional MacPherson suspension and approximately 10% lighter than a conventional twist-beam suspension. When compared to a steel leaf spring, the company’s composite version can be up to 60% lighter, according to ZF’s Gabriele Fruhmann, Project Leader for composite leaf spring rear suspension.

The transverse leaf spring layout enables the elimination of two conventional coil springs, the antiroll bar, mounts and links, as well as two control arms, Fruhmann said.

According to Werner Kosak, Vice President of ZF’s Global Chassis Systems Engineering, “one control arm on each side of the rear suspension is replaced by a composite leaf spring, and also because of the additional integration of stabilizer bar and coil spring, there is weight reduction and cost reduction.”

Micro and mini cars are prime targets of ZF’s wheel-guiding leaf spring. “Electric-drive vehicles are also good candidates for this technology because of the low weight of the leaf springs as well as the available packaging space in front of and above the leaf springs between the longitudinal links,” said Kosak.

The first production application of ZF’s rear suspension with composite leaf spring is possible as early as the 2014 model year, according to Kosak.

A lightweight suspension strut module with integrated wheel carrier has been a ZF Sachs development study project since early 2009.

In one design proposal, the strut, knuckle, and bellows spring are made of long-strand glass-fiber-reinforced plastic. The bellows spring replaces the conventional steel support springs.

“Our focus is a weight reduction of 50% with this new damper compared to a current series aluminum strut,” said Ron Griffith, Director of Engineering and Sales for Suspension at ZF Sachs Automotive of America.

The first application of the composite strut module with integrated wheel carrier is likely to be in the 2015 time frame on micro and mini cars, according to Griffith.

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