Active roll stabilisation in the form of the ACTIVE CURVE SYSTEM can be optionally combined with both the AIRMATIC air suspension with Adaptive Damping System (ADS) and the ON&OFFROAD package. This system uses active anti-roll bars on the front and rear axles, which it controls automatically as a function of the lateral acceleration, road speed and the ADS Comfort/Sport switch setting. The ACTIVE CURVE SYSTEM compensates for the roll angle of the body through bends, greatly increasing agility and driving pleasure in the process. The system has the additional effect of increasing handing stability and therefore safety, particularly at higher speeds. Further benefits of the ACTIVE CURVE SYSTEM include even greater ride comfort both when cornering and driving in a straight line, together with enhanced off-road abilities. The various control strategies in detail:

Comfort is improved when driving straight ahead as the rotary actuators decouple the two halves of the front and rear anti-roll bars in this situation, meaning that the anti-roll bars are "open" and do not react to a stimulus on just one side, such as bumps or potholes.
Increased ride comfort and more dynamic handling when cornering, because the system actively influences the anti-roll bars' torsional moments and twisting angles. The anti-roll bars' torsional moment furthermore remains constant in response to a stimulus on one side, such as is the case when driving over a pothole on the outside of the bend. Thanks to the individual control at the front and rear axles, distribution of the roll momentum can be varied, allowing the self-steering properties to be actively adapted to the prevailing driving situation. The handling characteristics are adjusted for extra agility when driving along country roads and for even greater stability on the motorway.
When driving in extreme off-road conditions at low speeds, the two anti-roll bars at the front and rear axles are decoupled. This leaves the anti-roll bars "open", allowing greater axle articulation.

The key componentry of the ACTIVE CURVE SYSTEM comprises a belt-driven hydraulic pump and an oil reservoir in the engine compartment, as well as a valve block and active anti-roll bars at both the front and rear axles. In contrast to a passive anti-roll bar, the active variant is split into two in the middle, and the two halves are connected with one another by means of hydraulic rotary actuators. Using the CAN signals relayed to it by pressure sensors and a lateral acceleration sensor, the electronic control unit regulates the hydraulic pressure.

The complex workings of the ACTIVE CURVE SYSTEM

The hydraulic pump feeds oil to the system from the oil reservoir. The pressure control valves and directional control valves integrated into the valve blocks at the front and rear axles set the desired pressure and twist the active anti-roll bars in the appropriate direction for the driving situation. Inside the hydraulic rotary actuators that are built into the active anti-roll bars there are six oil-filled chambers, three of which are pressurised for each direction of travel, i.e. a left or right-hand bend. The front valve block additionally assumes the task of distributing the oil flow between the two axles, irrespective of load.