Dawn of a New Axle Era
A little over forty years ago, the
1973: New suspension designs are gaining ground. Suddenly the future for rear-engine cars looks uncertain.
In Zuffenhausen and at the recently opened development center in Weissach, work is already well under way on a successor—the 928. It’s the first
Focus on driving safety
The Weissach axle—which stands for Winkel einstellende, selbst stabilisierende Ausgleichs-Charakteristik (angle-adjusting, self-stabilizing equalization characteristic)—allows
The first prototypes of the 928 also suffer from unstable self-steering tendencies. This is because lateral forces in curves cause the outer rear wheel to switch to a positive track, as if a person’s foot were turned out. What’s almost even worse is that releasing the accelerator during a curve causes a frontward shift in the car’s center of gravity, which lowers the load on the rear. Not only that—the effect of the engine drag torque on the wheels causes them to turn slightly outward. In right-hand curves, for example, the greater load on the left rear wheel will cause it to turn to the left, meaning that the wheels turn somewhat toward a “toe-out” position. The car oversteers when releasing the accelerator in curves.
A meticulous development process is launched under the direction of
Their painstaking adjustments pay off. “The Weissach axle suddenly gave the 928 much more stable self-steering properties because the car no longer oversteered,” recalls Frank Lovis, who was a test driver for
Harrer, too, finds it difficult to overstate the importance of the Weissach axle. “This pioneering work laid the foundation for modern axle kinematics, which have been continuously refined by
“We have a much more advanced understanding of material properties these days,” remarks Harrer. Rubber bearings are now elastomers: high-tech components with sophisticated chemical engineering and precision properties that have long since acquired progressive paths and whose enhanced damping qualities provide much greater suspension and acoustic qualities—throughout the car’s entire service life.
2018: Development work continues, in part because the benefits of the Weissach axle are constantly being adapted to new vehicle concepts and more compact installation spaces. These include SUVs like the
Despite all the electronic and active suspension control systems, there’s one thing Harrer doesn’t want to change. “Our cars will always have systems that balance out the axles. But thanks to modern simulation technologies, we no longer have to try out twenty different stabilizers, but maybe only three.”
However, the final touches at
By Klaus-Achim Peitzmeier
Photos by Stephan Lindloff,