Chassis can be intelligent too

“Everything was better in the past!” Some people say that about the music of the 1970s, others about fashion, and still others about the world of work — but nobody can really mean it about the chassis of older cars.

When the driver accelerated an older model, its front section would rise skyward, and when he braked it would bow down. During fast turns, the car body would lean outward alarmingly, and if the driver drove over a bump, one of the rear wheels was likely to lose contact with the road. The technology of that era was still fairly powerless against these physical effects, because the cars’ suspension system consisted of two passive components: the steel draw spring and the shock absorber. If the spring was soft, the ride comfort would increase, but driving stability would suffer. A hard spring would make the body more stable, but it took a toll on driving comfort.

The shock absorber’s task was to damp the spring’s effect — in other words, slow down the spring’s compression and extension. Without the shock absorber, the car would have leaped down the road like a horse in a meadow after being cooped up in the barn all winter. These two automotive components were not adjustable. That means the developers had to decide ahead of time which characteristics they wanted a vehicle to have.

No more bad vibrations

This was of course an annoying problem for the developers. As a result, in the late 1970s the company then known as Daimler-Benz AG applied for a patent for an active “spring-damping system.” An S-Class of the 126 model series was used for the driving trials of this system. The reasoning behind the system went as follows: If you replace the conventional compression springs and shock absorbers with quickly adjustable hydraulic cylinders, you can continuously adapt the car’s handling during a drive, so that it is always optimal for every situation. As a result, there’s no more troublesome rolling during curves and no more rocking on bumpy roads or during braking. Bobblehead dolls on dashboards became a thing of the past.

A revolution: The ABC suspension system

Nonetheless, several years of development work were necessary before ACTIVE BODY CONTROL, or ABC for short, was launched on the market in 1999. This suspension system celebrated its premiere in the most expensive vehicle in the Mercedes-Benz portfolio: the CL. Each one of the four suspension struts was a mechanical unit consisting of a positioning cylinder (also known as a plunger piston) and a steel spring. During the drive, this hydraulic system could adjust the plunger at lightning speed. Through this mechanism, the forces acting between the body and the wheels were permanently regulated in such a way that the body was ideally supported and damped.

Numerous sensors in the chassis control unit calculated how high the pressure on the spring should be and how long the pressure should be applied for. In addition to the car’s speed, the steering wheel angle, and the movements of the wheels, the vertical, longitudinal, and lateral accelerations were all recorded. Within milliseconds, a hydraulic pump then forced hydraulic fluid with a pressure of 200 bar into the positioning cylinder as needed. Note that the pump supplied each wheel individually according to its requirements.

The large Mercedes-Benz coupe CL 500/CL 600, which was presented in 1999, was the world’s first active vehicle with the Active Body Control ABC controlled suspension system.

In subsequent years, ABC was also available in the S-Class and the SL. Previous technology had only enabled a car to react to the situations arising during a drive. But that changed in 2013 with the introduction of the S-Class of the model series 222. The S-Class detected bumps in the road by means of a camera, raised itself up slightly in order to increase the spring travel, and reduced the spring preload when the bump was reached so that the car could gently glide over it. Typical S-Class — the car was in effect looking into the future when it used the ROAD SURFACE SCAN system. And because this was so remarkable, ABC received a new name: MAGIC BODY CONTROL.

In 2014 the CL once again reached a milestone: By means of a camera it now registered not only bumps in the road but also curves. After detecting a curve, it tilted the car into it by a few degrees, just like a motorcycle. This curve inclination function, called CURVE, was subsequently also installed in the SL and the S-Class.

The new GLE goes one step further

The previous ACTIVE and MAGIC BODY CONTROL systems used a hydraulic network that was supplied by a belt-driven pump. But the increasing electrification of the drivetrain — keywords 48-volt technology and the
beltless engine — meant that the combustion engine would more and more often stop running while driving. And in those moments even the best belt-driven pump would be useless.

Because the new GLE now for the first time has a 48-volt on-board electrical system and an active chassis, it has become the pioneer of E-ACTIVE BODY CONTROL. The E in its name indicates that this is an electrical system. In this system, the hydraulic pump is no longer driven by a belt. Instead, each suspension strut is supplied individually by an electric hydraulic pump with an operating voltage of 48 V.

Another new feature is the fact that E-ACTIVE BODY CONTROL is based on the air spring. These bear the car’s base load and control its level. The electrically driven hydraulic pumps are turned on only if additional power is needed — and that saves a lot of energy.

Why is a hydraulic system still needed? And why couldn’t the additional compressed air simply be forced into the suspension struts? The developers actually researched this possibility, but they finally abandoned it because it would have required a large reservoir of air and because the air would have been heated up because of the compression. Hydraulic technology, now operated with electric drive as needed, still offers unmatched performance and energy density.

Also effective off-road

Like its predecessor system, E-ACTIVE BODY CONTROL can of course also compensate for bumps in the road, and the CURVE drive program tilts the chassis by as much as three degrees when rounding a curve. In the case of a high SUV chassis, that makes driving along curving roads much more pleasant. The new system also offers spectacular features for off-road driving. If an overconfident GLE driver has gotten stuck in deep sand, by simply pressing the touchscreen he can activate the recovery mode. The car then jumps, hop by hop, out of the hollow . And when the individual wheel control is active, the driver can interactively change the height of each wheel separately, for example to make it easier to drive across a slope.

Incidentally, so far none of Mercedes-Benz’ competitors have been able to offer this kind of active chassis, whose adjustable stabilizers can simply decrease the curve angle when driving along curving roads. The new GLE will celebrate its world premiere in early October at the Autosalon Paris 2018.

Put to the test: The GLE in the test on the handling course

We have enabled a selected group of nine journalists from Germany and abroad to take a ride in the front-passenger seat of the new GLE and experience at first hand its three faces — off-road, on country roads, and on the handling course. The reviews in the media were unanimously very positive, confirming that our development team has reached its goal: building the world’s most intelligent chassis.

Michael Allner works as press spokesman in global communications for Mercedes-Benz Cars.