Compared with Citroen’s
Activa, Mercedes’ ABC (Active Body Control) seems rather simple. ABC
is purely an active roll control device. It can vary spring rate but
not damping, unlike Citroen’s Hydractive or Activa. Therefore it is
not classified as semi-active suspension. However, the application in
the new CL coupe demonstrate it helps achieving a stable and fluent
cornering. It also saves the need of anti-roll
bar.
New CL with ABC
versus old CL
After 20 years of research and development work,
Mercedes-Benz presented an actively regulated suspension system
that it claims makes driving even safer and more comfortable.
The system, termed Active Body Control (ABC) is fitted as standard to
the new Mercedes CL coupe and entered full-scale production from the
end of 1999
Mercedes-Benz says this new development is a major technical milestone
because it has solved the traditional suspension tuning conflict
between driving safety, dynamics and ride comfort. As a result, it
claims, Active Body Control is vastly superior to conventional passive
spring-damper systems.
With high-pressure hydraulics, sophisticated sensors and powerful
microprocessors, the active suspension system adapts the car body
springing to the actual driving situation in a split second. In this
way, Active Body Control reduces body movements by up to 68 percent
when starting from rest, cornering and braking.
The new Mercedes-Benz CL rounds bends with considerably reduced body
roll and swerves round obstacles at high speed with much greater
safety than cars with conventional suspension technology, says Benz.
In the slalom test, the dynamic body roll tendency is up to 50 per
cent below the values of the outgoing CL model with passive springing
and damping.
The driver of the new CL can select the desired suspension setting by
pressing a button on the centre console. The "Comfort"
program, offers the ride comfort of a saloon, while the
"Sport" setting characteristics are akin to those of a
sports car.
In this mode, body roll when cornering is reduced by a further 27per
cent - compared to "Comfort" mode .
Active Body Control is based on interplay between electronic,
hydraulic and mechanical components. Sensors monitor the levelling
position and body acceleration so that the microcomputers are
constantly supplied with instantaneous data.
With the aid of the sophisticated sensor system, Active Body Control
detects the movements of the car body even as they start and corrects
them within a fraction of a second.
Body movements are corrected by hydraulically driven servo cylinders
in the suspension struts. These "plungers" are located
between the coil springs and the body and apply additional forces in
response to computer commands. This regulates the action of the
springs as a function of body movements at intervals of only ten
milliseconds.
The adjustment range of Active Body Control is limited to car body
movements up to a maximum of five Hertz. These vibrations are
generally caused by uneven roads or when braking or cornering.
For the higher-frequency vibrations of the wheels, Mercedes-Benz
continues, as before, to use passive gas-pressurised shock absorbers
and coil springs, but with comfort-oriented tuning.
The absence of stabiliser bars at both front and rear (made possible
by the active suspension system) also has a positive effect on ride
comfort. |
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