Active Roll Stabilization from ZF

30.01.2008 -- A two-ton vehicle capable of handling tight turns with high-performance sports car agility? And rock-solid directional stability? This isn’t sleight of hand. It’s the art of automotive engineering. ZF specialists made this possible by concentrating on a key suspension component: stabilizers.

ZF's Active Roll Stabilization

Cars tend to lean to one side, or sway in a turn. While the vehicle starts to “dive” on the outer radius of the curve, the inner wheels lose their grip on the road surface. The faster the vehicle, or higher the center of gravity, the more it will sway in a cornering situation. This apparent physical limit at which driving dynamics and enjoyment come to an end for full-size sedans and SUVs is well known, and is something that has disgruntled ZF suspension specialists for a long time.

In an effort to improve directional stability on winding roads, ZF engineers focused on a key suspension component: stabilizers. Attached to the front and rear axles, stabilizers are designed to even out the compression of the springs on the left and right wheels. This operation is purely mechanical. A metal bar connects the left and right wheel suspension. But the question, how hard or soft a conventional stabilizer bar should be, often leads to conflicting opinions among chassis designers. An extremely stiff stabilizer is good for reducing vehicle roll. The disadvantage is that it transfers the suspension response to road surface unevenness on one side to the other side of the vehicle. Additionally, stiffer antiroll bars on the front axle cause the vehicle to understeer.

The ideal solution is an active, variable stabilizer. ZF Sachs has been developing the Active Roll Stabilization (ARS) system since 2001. This system is currently available in BMW models under the name Dynamic Drive and is also used in an SUV. ARS is based on a hydraulic oscillating motor mounted near the center of the stabilizer bar. Activated by sensors and an electronic control, the oscillating motor creates torsion and thus adapts the stabilizer to the driving situation. The result is impressive: with lateral acceleration up to 0.5 g, the system fully compensates body roll. As a result, the vehicle remains absolutely parallel to the road surface. For example, ARS enhances driving dynamics in the highly successful SUV segment. ARS also improves self-steering properties. And this increases steering precision.

Source: ZF