E-ACTIVE BODY CONTROL suspension system: The car that eliminates poor roads

Jun 24, 2019
Stuttgart/Salt Lake City

Even better ride comfort and agility, plus completely new functions such as free-driving mode, are provided by the optional E-ACTIVE BODY CONTROL suspension, which is now combined with the newly developed AIRMATIC air suspension. This is the only system in the market that can individually control spring and damping forces at each wheel, suppressing rolling, pitching and lifting movements. Together with Road Surface Scan and the curve inclination function CURVE, E-ACTIVE Body Control makes a quite exceptional level of comfort possible, underscoring Mercedes-Benz's aspiration to build the world's most intelligent SUV suspension.

Active suspension systems have a long tradition at Mercedes-Benz. More than 40 years ago, research was already being conducted on spring and damper systems that would allow the power at each wheel to be individually controlled. The objective: to improve both ride comfort and vehicle dynamics. ABC (Active Body Control) first entered series production in 1999. In subsequent years ABC was continuously developed further, with the ROAD SURFACE SCAN function added in 2013 to produce the first predictive suspension that already responds to surface undulations before they are reached.

E-ACTIVE BODY CONTROL continues this tradition in a unique way. Developed by Mercedes-Benz in-house, it runs on 48 volts and is available in the GLS as an optional extra. The system is based on the full AIRMATIC air suspension system, and therefore offers all-round level control which keeps the vehicle level constant irrespective of the load. The level can also be raised or lowered as required, to increase ground clearance. Different levels can also be selected in special off-road driving modes.

Furthermore, the hydropneumatics generate dynamic forces that overlay the air suspension forces and actively support and dampen the vehicle body, e.g. during linear and lateral acceleration or when driving on uneven roads. The body no longer squats or pitches during braking and acceleration, and on poor road surfaces the system is even able to recuperate energy, roughly halving the energy requirement compared to the preceding system in the S-Class.

The active suspension also allows a very wide spread of handling characteristics that can be set with the driving mode – from the comfort of a luxury saloon to the agility of a sporty SUV. In addition, the engineers have realised a number of entirely new functions for the GLS:

  • Rocking mode: If the GLS has become bogged down in a sand dune, for example, this mode - which is only available in the Off-Road drive mode - can help to free the vehicle more easily in many such situations. If possible, the suspension level is automatically raised and lowered several times, thus alternately increasing and reducing the ground pressure of the tyres and improving traction – the GLS rocks itself free.
  • Individual wheel actuation: Individual wheel actuation is another new function for off-road driving. After selecting the Off-Road drive mode, the ride height at each wheel can be individually adjusted via the touchscreen of the media display, thus improving the vehicle's off-road focus in rough terrain when e.g. one wheel is stuck in a ditch or a wheel spring is fully compressed.
  • Rear-end lowering when loading/unloading: When the button for rear-end lowering in the luggage compartment is pressed, the vehicle is lowered to a defined level at the rear axle. This allows the luggage compartment to be more conveniently loaded and unloaded. The level at the front axle remains unchanged. The rear axle is lowered by about 50 mm from its currently set ride height, but not lower than -70 mm. This function is not activated when a trailer is hooked up.

In addition, E-ACTIVE BODY CONTROL in the GLS has functions already familiar from the S-Class, which have been further advanced:

  • Curve tilting function: In CURVE drive mode, the GLS actively leans into bends by up to 3° in three stages, like a motorcycle. This reduces the lateral forces acting on the occupants. Cornering is therefore made much more pleasant, especially for the front and rear passengers.
  • ROAD SURFACE SCAN: If the GLS is equipped with a stereo multi-purpose camera, it continuously monitors the road surface ahead of the vehicle. The suspension struts are then activated so as to substantially reduce the body movements when driving over surface undulations, as the suspension responds even before the uneven stretch is reached. This enhances the comfort in particular away from paved roads.

Operating principle: How E-ACTIVE Body Control works

E-ACTIVE BODY CONTROL in the GLS supplements the air suspension with semi-supporting hydropneumatics. The air springs bear the base load of the vehicle body and gradually regulate the level. The hydropneumatics generate dynamic forces that overlay the air suspension forces, and actively support and dampen the vehicle body.

At each wheel, a damper is installed within the axle whose two working chambers have an adjustable damping valve and a hydraulic pressure reservoir. The damper is connected to an intelligent motor/pump unit in the 48 V network by hydraulic lines. Actuation of the motor/pump unit enables the hydraulic fluid to be displaced to create a difference in pressure within the damper, allowing an active force to be generated.

The motor/pump units at all four wheels are coordinated by a central control unit which also actuates the valves and the compressor for the air spring, and therefore always controls the entire suspension system.

The transition from a belt-driven hydraulic pump to an electric 48-volt pump also takes into account the increasing electrification of the powertrain: the combustion engine is idle increasingly often – or not used at all.