Chassis and suspension: Agile steering, active suspension, adaptive brakes

Sep 7, 2010
  • New: Active Body Control with crosswind stabilisation
  • Direct-Steer system enhances driving pleasure
  • Torque Vectoring Brake: more stability, more dynamism
  • Electronically controlled brake system ADAPTIVE BRAKE
The new-generation CL remains a masterwork among the luxury coupés in regard to handling dynamics, road roar and tyre vibration characteristics and agility. The Mercedes-Benz developers achieved this with a number of new developments and improvements like the Direct-Steer system, whose variable ratio depends on the steering angle, and the modified Active Body Control (ABC) with crosswind stabilisation.
New with crosswind stabilisation: Active Body Control
The basis for the agile handling of the CL, which allows no compromises on suspension comfort, is the Active Body Control suspension (standard for CL 500 BlueEFFICIENCY and CL 600) with which Mercedes-Benz opened up new dimensions in handling dynamics in 1999 in the CL Coupé of previous C 215 model series. Since then the Sindelfingen engineers have developed the system consistently further with every model change and facelift so that eleven years down the road it still marks the peak of suspension engineering. For the new-generation CL the suspension specialists complemented the Active Body Control with a crosswind stabilisation function.
In strong gusts of crosswind, and depending on the direction and intensity of
the wind having an effect on the vehicle, this system varies the wheel load distribution in such a way that the effects of winds are largely compensated or reduced to a minimum. For this purpose the ABC control unit uses the yaw rate, lateral acceleration, steering angle and road speed sensors of the Electronic Stability Program ESP®.
The system filters out weak crosswind signals, only coming into action when a certain threshold has been exceeded. In this case the driver is assisted by a change in the diagonal wheel load distribution, for example affecting the left front wheel and the right rear wheel. Specialists refer to this as Active Body Control crossover. The resulting steering effect is sufficient to reduce the effect of the crosswind.
Crosswind stabilisation is active at speeds above 80 km/h, when travelling straight ahead or taking gentle corners. If the driver takes purposeful and immediate corrective action himself, the function deactivates itself. Trials with test drivers, in which wind conditions akin to hurricane speed were simulated, elicited a positive response from all those involved.
Designed to balance the car in a flash: the suspension cylinders
Technical background to ABC: In this Mercedes-Benz active suspension system, the four spring struts are equipped with microprocessor-controlled plunger cylinders that can almost completely compensate for lifting, rolling and pitching of the body. The computer uses various acceleration sensors to obtain information on the current driving situation, and compares these data with those from the pressure sensors in the spring struts and the level sensors on the control arms. The system then computes the control signals, which the servo-hydraulic valves at the front and rear axle transform into precisely metered oil flows.
Once oil flows into the plunger cylinders, this modifies the tracing point of the steel springs integrated into the spring struts, generating the necessary force to counteract the body movements.
Whereas up to now ABC worked with a constant hydraulic pressure, in the CL 500 BlueEFFICIENCY for the first time a dual-pressure concept is employed: in the main circuit a permanent pressure of 185 bar prevails, to which a secondary circuit with maximum 10 bar hydraulic pressure is added as new feature in the hydraulic pump. By means of an additional control valve, at traffic lights or on smooth, straight roads ABC can change from main to secondary circuit. At the same time the pump is switched off. Advantage of the new system: the hydraulic pump requires less energy, which takes load off the engine and cuts fuel consumption. The savings effect is 0.2 litres of premium petrol per 100 kilometres (NEDC combined cycle).
At the touch of a button: individual suspension characteristics
The CL offers the possibility of changing the characteristics of transmission and suspension, independently of each other, from comfortable to sporty. The switch for the transmission tuning is located on the centre console next to the COMAND Controller; the switch to activate the Sport mode of the Active Body Control and die AIRMATIC electronically controlled damping system (CL 500 4MATIC BlueEFFICIENCY only) is positioned on the control panel between instrument cluster and COMAND display.
For the suspension, the driver can choose one of two modes:
  • Comfort: Active Body Control and AIRMATIC operate in Comfort mode to comfortably absorb bumps and ripples.
  • Sport: bumps and ripples are absorbed, but with a tauter touch.
The independent control of the transmission and suspension modes gives the driver yet more freedom to determine the overall characteristics of the Mercedes coupé. Along with the "classic" combination of sporty suspension and transmission characteristics, in future the driver has the opportunity, for example, to combine a fuel-saving ECO transmission mode with a sporty, taut suspension, or to travel with a comfort-enhancing damper configuration and sporty transmission mode.
If the CL is travelling on poor roads that call for higher ground clearance, the driver can raise the body by 45 millimetres at the touch of a button. At high speeds, in the Sport mode ABC lowers the body automatically by as much as ten millimetres to reduce wind resistance and fuel consumption.
Direct-Steer system: more cornering enjoyment and steering precision
The new Direct-Steer system of the CL was developed from the familiar speed-dependent steering that Mercedes-Benz offers for many of its models. In this case the steering effort depends on the vehicle speed – the effort required increases with the speed. In practice this means more steering comfort during parking manoeuvres, which then require less effort, and more safety at higher speeds where a greater steering effort ensures safe straight-line stability, for example
on motorways.
The new Direct-Steer system retains these positive attributes of speed-sensitive steering and adds a variable steering ratio to them. This changes depending on the steering angle. The ratio is normal when the steering is more or less centred, which makes for good straight-line stability and therefore safety. The steering ratio changes very rapidly to become more direct as soon as the steering angle reaches five degrees, reaching its end value at a steering wheel angle of 95 degrees, where the steering feels very direct. Only relatively small movements of the wheel are then required to make course corrections. With the Direct-Steer system, the number of turns of the steering wheel required from stop to stop is reduced by around 25 percent.
The perceived effect of Direct-Steer is however even more important than measured data. Even at inner-city speeds the driver needs to turn the wheel less frantically, with changes of direction faster and involving less effort. Winding country roads also become the natural habitat of the Mercedes-Benz luxury coupé equipped with Direct-Steer, as very small steering wheel movements are necessary to steer the car.
Rapid sequences of bends can be mastered almost intuitively safely and precisely, and with enormous enjoyment. This all adds up to considerably more agile handling.
Purely mechanical: variable steering ratio
Despite its remarkable effect, the key component of the Direct-Steer system is simply a steering rack. Its secret lies in the teeth cut into it. Starting from the neutral position for driving straight ahead, they are spaced increasingly farther apart. The change in steering ratio is therefore produced by purely mechanical means. With this solution, Mercedes engineers have been able to dispense with the complex actuators and sensor systems used by other variable steering systems. The advantages include very low susceptibility to faults and low weight. Moreover, the system always responds predictably and in the same way, while other variable steering systems sometimes require rapid adaptation by the driver in rapidly changing situations.
Another comfort feature: the height and lateral position of the telescopic steering column of the CL are electrically adjustable. As an additional convenience, the steering column automatically helps the driver enter and leave the vehicle. After the driver withdraws the electronic ignition key, the steering wheel moves upward, increasing the available legroom. The steering wheel remains in this position until the key is once more inserted into the ignition switch, at which point it returns to the previous position, which is remembered.
Torque Vectoring Brake: ESP® helps with the steering
Extra safety at the physical limits, as well as even more agility, is provided by the Torque Vectoring Brake in the new-generation CL – targeted, one-sided braking intervention at the inside rear wheel when cornering. If ESP® detects a tendency to understeer, the newly developed Torque Vectoring Brake adopted from the
S-Class saloon generates a defined turning or yawing moment around the vehicle's vertical axis within fractions of a second. Thanks to the different torque distribution that results, the CL turns into the bend under precise control without any loss of handling dynamics. The advantage of this solution over complex mechanical components such as an active steering rear axle, additional multi-disc clutches or an active differential: the Torque Vectoring Brake can be implemented
without an increase in vehicle weight and therefore no disadvantages in terms of fuel consumption. This Torque Vectoring Brake function is standard equipment in the new generation CL.
ADAPTIVE BRAKE: high-tech brakes for maximum safety
The Mercedes-Benz CL also is the benchmark where its braking system is concerned: thanks to electronic control of the hydraulic dual-circuit brake system, the standard ADAPTIVE BRAKE allows assist functions that enhance safety and comfort. These include priming of the braking system in critical situations: when the driver changes abruptly from the accelerator to the brake pedal prior to emergency braking, ADAPTIVE BRAKE increases the pressure in the brake lines to bring the brake linings close to the discs so that they are able to engage instantly, and with full force, when the brake pedal is operated. In this way the system supports the standard Brake Assist and Brake Assist PLUS (BAS PLUS).
ADAPTIVE BRAKE also has safety benefits in the wet: the system briefly applies the brakes at regular intervals to wipe the film of water from the brake discs and ensure that the brakes are able to perform at their peak. This automatic brake drying function is always activated when the windscreen wipers of the CL have been operating for a certain length of time. The finely metered brake pulses are imperceptible to the driver.
After the vehicle has been braked to a standstill, briefly pressing the brake pedal a little further is all that is required to activate the HOLD function.
The coupé is then held by the brakes, even if the driver's foot comes off the brake pedal. In this way ADAPTIVE BRAKE prevents the car from rolling forward inadvertently when stopped at traffic lights or stuck in stop-and-go traffic, and from rolling back when facing a slope. The HOLD function is deactivated automatically when the car moves off again.
Very vigorous: extra-large brakes
Large brake discs at the front and rear provide the technological basis for safe and reliable deceleration using ADAPTIVE BRAKE. Depending on the engine installed, the disc diameters range up to 360 millimetres at the front and up to 330 at the rear. The front brake discs are perforated for all model variants. The perforations shed moisture and dirt, which increases the brakes' reliability and maintains their excellent deceleration values even in inclement weather conditions. A 9.5-inch tandem brake booster satisfies high standards for responsiveness and ease of use.
Braking system data for the Mercedes-Benz CL
Front axle
CL 600
Brake calliper
Pad area
Brake dis
Diameter Thickness
4-piston fixed calliper
2 x 77 cm²
Internally ventilated, perforated
350 mm 32 mm
6-piston fixed calliper
4 x 120 cm²
Internally ventilated, perforated
360 mm 36 mm
Rear axle
Brake calliper
Pad area
Brake disc
Diameter Thickness
1-piston floating calliper
2 x 38 cm²
Internally ventilated
320 mm 24 mm
4-piston fixed calliper
2 x 48 cm²
Internally ventilated
330 mm 26 mm
The Mercedes-Benz CL also features an extremely easy-to-use electric parking brake as standard. Pressing a button on the dashboard is all that is needed to activate the brake. If the driver engages a gear and drives off, the brake is automatically released. The key components of this system are two separate servo drum brakes on the rear wheels and an electric motor with speed-reducing gear that applies the brake shoes by means of cables. The electric parking brake can also be engaged if the engine is switched off.
Standard: tyre pressure loss warning system
Tyre pressures in the CL are monitored by the Electronic Stability Program ESP®, or by a special system based on radio technology:
  • ESP® continually compares the speeds of the wheels, which are mainly dependent on the road speed, the load and the tyre pressure. In addition, the control unit automatically checks other dynamic performance criteria such as lateral acceleration, yaw rate and wheel torque, in order to identify any loss of pressure in a tyre. In doing so, the system detects any anomalies and informs the driver via a message on the central display panel: "Tyre pressure, check tyres". The tyre pressure loss warning system based on ESP® technology is included in the standard equipment of the CL.
  • In the tyre pressure monitoring system (optional), a sensor measures both the air pressure and the air temperature inside the tyre and transmits the data by radio at regular intervals to an underbody receiver aerial. Intelligent software automatically identifies the positions of the wheels so that the driver is provided with information about the air pressure in each of the four tyres via the central display panel.
Effortless progress in any weather: the 4MATIC all-wheel drive
Mercedes-Benz offers 4MATIC all-wheel drive for the CL 500 BlueEFFICIENCY. The centrepiece is a centre differential with a planetary gear set. The permanent, defined torque distribution of 45:55 percent between the front and rear axles ensures reliable and predictable driving characteristics on all road surfaces. An integrated multi-disc clutch guarantees even more traction and optimal handling stability with the onset of slip.
Mercedes-Benz combines 4MATIC with the Electronic Stability Program ESP®
and the traction system 4ETS, which specifically brakes spinning wheels and transfers the torque to the wheels which still have good traction. The system uses sensor signals to meter the automatic braking impulses that increase traction when moving off on slippery surfaces and can improve handling in critical situations. 4ETS achieves the effect of conventional differential locks and provides more comfort than the technology used in other all-wheel drive vehicles.
Owing to its compact, lightweight, low-friction design, 4MATIC all-wheel drive has definite advantages over other systems in terms of weight, fuel consumption, comfort and passive safety. Depending on the engine variant, this all-wheel drive technology incurs an unrivalled, low weight penalty of only 70 kilograms.
Strong team: AIRMATIC air suspension and Adaptive Damping System
AIRMATIC air suspension is included as standard in the CL 500 4MATIC BlueEFFICIENCY. Mercedes-Benz combines this with the Adaptive Damping System (ADS), which continuously regulates the shock absorber characteristics and takes the road conditions, driving style and vehicle load into account. The system adapts the damping forces for each individual wheel to the current situation within just 50 milliseconds. As in the variants with Active Body Control, the driver can individually adjust the ride height and the suspension and transmission characteristics.