When automobile manufacturers present their own vehicles, the German premium manufacturer prefers to remain silent about the role of suppliers. Understandable, because if you look under the sheet metal, you'll see that many components don't have the manufacturer's label on them, but rather that of a supplier. For example, the two letters of “ZF”.
Performance, made by ZF
560 PS strong, 318 km / h fast, in 3.1 seconds from 0 to 100 km / h. The Porsche 911 Turbo S is the heart-jack in every car quartet and on the road, it demonstrates with absurd lateral acceleration what is possible with a production car.
When it comes to the 200-meter slalom course, the Turbo S disassembles the rest of the fraction with incredibly agile handling. Hardly thought, hardly turned, the 911 Turbo S changes direction. Its front axle always remains agile, handy and noticeable - which, however, is also due to the rear axle. And that's where the rear axle steering from ZF works in the Turbo S. Her name: AKC.
Rear axle steering in the Porsche 911 Turbo S
Due to the rear-engine principle, the rear-axle steering (Active Kinematics Control) in the Porsche 911 Turbo is a little more complicated than basically necessary. Two actuators each sit on the left and right in the area of the rear axle suspension and move the axle kinematics via struts.
The actuators are able to operate at a speed of 40 mm / sec and move a maximum of 13.5 mm within the axis kinematics. This corresponds to a toe angle change of a maximum of 3 °. Three degrees are heard, if one compares that with the front axle, first of all little. However, the effects of the rear axle on the driving stability are enormous and so act the 3 ° with noticeable agility increase.
The effect is impressive. And the rear axle steering can improve both: agility and stability!
Up to around 60 km/h, the rear axle steers in opposite directions, which increases agility and accelerates the steering reaction. In addition, the rear wheels begin to steer with the front axle, which in turn increases stability. This effect can ensure a high level of driving stability, especially when changing lanes quickly at high speeds. The change in direction occurs smoothly and is calculated by the control system from dozens of parameters. The system is controlled via an electronic controller. In principle, rear axle steering is a “drive-by-wire” solution.
BMW and Audi also rely on ZF all-wheel steering
In the new Audi Q7, all-wheel steering minimizes the turning circle and increases the handiness of the large SUV. Here a central module works in the middle of the axis. Both rear wheels are controlled from there. The maximum track adjustment here is 5 °. The current five-seater BMW has rear-axle steering with a maximum steering angle of 3 °.