TechTalk

Published on July 15th, 2019 | by Daniel Sherman Fernandez

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Have you heard of Active Body Control?

Here is how Mercedes-Benz delivers that ‘magic carpet ride’ owners talk about.

This is product of Mercedes-Benz. Mercedes-Benz engineers have for years worked at delivering the ride comfort that has been legendary with Citroen cars using hydraulic suspension system. So now, the top end Mercedes-Benz vehicles come equipped with what Mercedes calls an ‘active body control’ (ABC) system. The active body control is a system designed and implemented by Mercedes that plays a critical role in the car’s overall function.

So What Does the Active Body Control System Do?

The active body control system is a type of suspension designed by Mercedes-Benz that is meant to help control the vehicle’s movement, stabilizing it while it taking sharp turns, using horsepower, or quickly applying the brakes. This type of suspension utilizes hydraulic fluid and is made up of many different parts and components.

Year 1999 Mercedes CL-Class

Introduced in 1999, Mercedes-Benz first showed ABC in the CL-Class. After 20 years of research and development it was the solution to the traditional problem associated with the tuning of a passenger car chassis: should wheel vibrations caused by the road surface be kept to a minimum by a sporty, stiff shock absorber configuration, or should the damping be made more comfortable and soft at the expense of handling safety and performance?

Thanks to Active Body Control, this conflict of aims is a thing of the past; the suspension configuration is automatically adapted to suit the current driving situation. A high level of comfort is accompanied by dynamic performance – or vice versa.

To this end, the four spring struts are equipped with microprocessor-controlled plunger cylinders which almost completely compensate yawing, pitching and rolling movements of the vehicle body. The computer receives information about the relevant driving situation from the various acceleration sensors, then compares this with the data from the pressure sensors in the spring struts and the level sensors in the steering control arms. The ABC system translates this information into control signals, which are implemented as precisely metered oil flows by hydraulic servo-valves on the front and rear axles. When oil flows into the plunger cylinders, these adjust the tracing point of the steel springs integrated into the spring struts, generating the forces necessary to counteract movements of the vehicle body.

Body is stabilised within fractions of a second

Owing to the constantly available hydraulic pressure of up to 200 bar, ABC is able to stabilise the vehicle body practically immediately – within a fraction of a second. The system operates in the vibration range of up to five hertz, the range which causes pitching and rolling movements on uneven road surfaces, side-roll on bends and the typical body dive experienced during braking. Higher-frequency vibrations and wheel damping are the responsibility of passive twin-tube gas-pressure shock absorbers, which can be configured for excellent comfort.

Mercedes-Benz has enhanced Active Body Control over the years and with the last CL-Class and made it even better. Each component has been reworked. The specialists have now arranged various components into groups, in order to improve the control functions with shorter connecting lines and reduce the installation space required.

Body roll reduced by up to 45 per cent when cornering at speed

The major advantage of second-generation Active Body Control, however, is its greater efficiency in reducing body movements to correspond to the driving situation. This is where the Mercedes coupé advances into new dimensions of handling – while simultaneously offering greater comfort that every driver will immediately notice. The body roll angle, for example, is reduced during a dynamic driving manoeuvre by more than 45 per cent – from the previous value of 2.2 to 1.2 degrees. When cornering at speed – for example when leaving a motorway – this second-generation ABC suspension reduces the roll angle to just 0.7 degrees.

Other special features of Active Body Control include variable anti-roll control between the front and rear axles, which the system carries out automatically in accordance with the vehicle’s speed. The system also takes the vehicle load into account: on the basis of the plunger and spring travel, the ABC computer calculates the actual vehicle weight and takes it into consideration for the active control function.

Individual suspension and transmission characteristics

In addition, Mercedes vehicles equipped with ABC features an S/C/M button in the centre console with which the driver is able to modify the overall characteristics of the vehicle from “comfortable” to “sporty”:

·             Comfort: In this mode the automatic transmission changes the gears at lower engine speeds, and the CL coupé moves off in second gear. The ABC suspension operates in Comfort mode, comfortably smoothing out uneven road surfaces and bumps.

·             Sport: The automatic transmission makes full use of the engine speed range in this setting. The ABC suspension operates in Sport mode as well, with a stiffer damping effect on uneven surfaces and bumps. The characteristic map of the accelerator is also modified, so that the engine responds more rapidly when acceleration is required.

·             Manual: The automatic transmission is operated manually using gearshift buttons on the steering wheel, with significantly reduced gearshift times compared to the Sport mode. The suspension configuration selected by Active Body Control is the same as in Sport mode, as is the characteristic map of the accelerator.


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