The ABCs of Ride Control

2007 Mercedes-Benz CL-Class Coupe
(Photo: DaimlerChrysler)STUTTGART, GERMANY - The new 2007 Mercedes-Benz (M-B) CL-Class coupe features advanced chassis technology - Active Body Control (ABC) - as standard equipment. The system adjusts the suspension to the driving situation within a fraction of a second, providing superior handling while also ensuring a high level of comfort.  ABC was originally introduced in 1999, after more than two decades of research and development. M-B says it provides a solution to the traditional problem associated with the tuning of a passenger car chassis rides: optimizing safety, performance and comfort by allowing the suspension to be configured to automatically adapt to changing driving situations.  To accomplish this, the four spring struts are equipped with microprocessor-controlled plunger cylinders that almost completely compensate yaw, pitch and the 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, they adjust the tracing point of the steel springs integrated into the spring struts, generating the forces necessary to counteract movements of the vehicle body.  Optimizing the ride In developing the second-generation ABC system, engineers focused on improving handling and performance, while refining occupant safety and comfort:

Active Body Control
(Photos: DaimlerChrysler)

* Body stabilization within fractions of a second. Owing to the constantly available hydraulic pressure of up to 200 bar, ABC is able to instantly stabilize the vehicle body, says M-B. The system operates in the vibration range of up to 5 Hertz, the range that 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 controlled by the passive twin-tube gas-pressure shock absorbers, which can be configured for comfort. 

* Quicker response time. For the new coupe, M-B has reworked each ABC component to achieve better performance. Engineers have arranged various components into groups in order to improve the control functions with shorter connecting lines and reduce the installation space required. 

* Reduced body-roll in any driving situation. The second-generation ABC system provides up to 45 percent greater efficiency in reducing body-roll - even when cornering at speed. M-B says this results in improved handling, without sacrificing ride comfort. When leaving a motorway, for example, the suspension reduces the roll angle to just 0.7 degrees. 

* Variable anti-roll control between the front and rear axles. A further enhancement to safety and control is the variable anti-roll control feature. The system calculates the vehicle load weight, on the basis of the plunger and spring travel, and automatically adjusts the suspension relative to the vehicle's speed. Fingertip control  In addition to the ABC suspension features, the center console of CL-Class coupes feature an "S/C/M" button, which enables the driver to choose individual suspension and transmission characteristics to suit personal preferences on any given route. Drivers essentially choose how they wish the transmission to operate - comfortable, sporty or manual - and the ABC system does the rest.  In the Comfort mode, the automatic transmission changes the gears at lower engine speeds, and the CL coupe moves off in second gear. The ABC suspension is designed to comfortably smooth out the ride on uneven road surfaces and bumps.  If the Sport mode is selected, the automatic transmission makes full use of the engine speed range. The ABC suspension shifts to 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.  If the automatic transmission is set to Manual mode, the driver shifts manually by using gearshift buttons on the steering wheel, with significantly reduced gearshift times compared to the Sport mode. The ABC suspension configuration is the same as in Sport mode, as is the characteristic map of the accelerator. When traveling on poor roads where a higher ground clearance might be desired, the driver is able to raise the coupe's suspension by 45 millimeters. When traveling at high speed in Sport mode, ABC automatically lowers the suspension by up to 10 millimeters to reduce aerodynamic drag and lower the fuel consumption.(Source: DaimlerChrysler)