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Chassis: Solid Foundation
OverviewAt a glance: Technical highlights of the new S-Class*Body and Passive Safety: New MasterpieceChassis: Solid FoundationDesign: Effortless styleDriver assistance systems: Intelligent co-pilotsEngines and transmission: Strong performanceInterior: Man and machine in harmonyModel range: Peak of perfectionTechnical data S-ClassThe new Mercedes-Benz S-Class: Superlative in design and technology
- Axles and steering enhanced
- AIRMATIC with agile handling and even greater comfort
- Performance of Active Body Control significantly improved
- New ADAPTIVE BRAKE system with assistance features
- ABS, ASR and ESP® even more effective
With regard to handling properties, one is entitled to expect more from a Mer-cedes long-distance saloon than “ merely” exemplary comfort. The ActiveSafety and driving dynamics must meet equally high standards.
The S Class has always satisfied these expectations, but in the new saloon the Mercedes engineers have implemented additional advances and surpassed the high standard of the predecessor model in all aspects of chassis engineering. The most remarkable results - which drivers can feel with every kilometre - are in the areas of driving and suspension comfort, steering precision and agility, and driving and braking stability. Various enhancements and new developments con-tribute to these improvements, but the giant leap forward achieved by Mercedes-Benz with its new flagship model has only been made possible by the intelligent combination of all the systems and by their precise coordination and dependable interaction.
The larger track width relative to the predecessor model (+26 millimetres in front, +32 millimetres in the rear) and the longer wheelbase ( +70 or +80 millimetres), sat-isfy some important preconditions for the even better driving comfort of the S Class.
|Wheelbase mm||3035 or 3165|
|Track width front mm||1600|
|Track width rear mm||1606|
Front axle: four-link technology improved yet again
During the early phase of chassis development, extensive studies were done in-volving various axle designs. The results of digital design and testing methods and the extensive field trials provided the Mercedes engineers with confirmation that the four-link technology on the front axle offers the most benefits. Develop-ment then continued on the details of this design - particularly with regard to comfort.
The wheels of the front axle are controlled by what the engineers call an “upper link suspension”. It consists of an aluminium transverse link in the upper link plane, an aluminium tension strut below and a forged-steel spring rod. The two link planes are connected to each other by steering knuckles. The fourth compo-nent, and the one that accounts for the name of the “four-link” suspension, is the tie rod. It forms the connection between the front wheels and the transversely situated rack-and-pinion steering.
One essential benefit of this Mercedes four-link suspension is the elimination of the lower link plane. It enables good axle kinematics and is almost completely in-sensitive to vibrations caused by wheel imbalance or fluctuations in braking force. Starting from this good foundation, the engineers retuned the kinematics and elastokinematics and optimised them in comparison with the predecessor model. The safety specialists at the Mercedes-Benz Technology Centre also pro-vided an important reason to opt for the four-link system. The advantage for safety is that it offers larger deformation paths than other axle designs in the area of the lower link plane and can therefore absorb kinetic energy more effectively in the event of a frontal crash.
As before, the steering gear is located in front of the wheel’s centre and is thus in a position that supports the easily controllable, understeering effect of the Mer-cedes saloon in curves. The power rack-and-pinion steering has a variable trans-mission ratio (50.1 to 60.5 millimetres per steering wheel revolution) that oper-ates somewhat more indirectly in the middle of the range than at the peripheral settings. Comfort is considerably enhanced by the parameter feature that comes as standard: the lower the speed, the greater the power assistance. Below 200 km/h, the steering wheel torque diminishes continuously as a function of the driving speed, so that the driver need apply only about a third of the maximum steering effort during slow parking manoeuvres. The variable steering centring is a completely new feature of the S Class: The electro-hydraulic parameter servo valve is used to generate a centring moment that increases with the speed and gives the driver a secure and stable feeling in the straight-ahead position. In slow driving, this additional steering moment is not activated, and the benefits of the speed-dependent parameter steering can thus be fully exploited.
The height and lateral position of the telescopic steering column 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.
For the new S Class, Mercedes-Benz developed a four-spoke steering wheel with a diameter of 390 millimetres. Structurally, it consists of a magnesium pressure die casting that deforms by design in a frontal collision to reduce the risk of injury to the driver. With its illuminated control buttons integrated for maximum accessi-bility and ease of operation, the steering wheel is an important component of the overall scheme of control design in the new S Class. An electric steering wheel warmer is available as an option.
Rear axle: one hundred per cent aluminium
Since the multi-link independent rear suspension remains unsurpassed, the Mercedes engineers used it faithfully in the new S Class too. They improved some of the details, however. The rear-axle member, for instance, is a completely new development. In contrast to the previous version, it is now an aluminium structure open to the front, with a bolted front cross-bridge. The essential benefits of the new suspension sub-frame are its lower weight, greater strength and more compact dimensions.
Through their systematic pursuit of a lightweight design, the Mercedes engineers significantly reduced the weight of the unsprung masses at the rear axle, thereby improving handling and driving comfort alike. Four of the five suspension links consist of forged aluminium. The spring rod was designed from a single section of aluminium plate, and the hub carrier consists of die-cast aluminium. In addition, the rigidity of the wheel-guiding components was increased.
The specialists in Sindelfingen also devoted attention to decoupling vibrations that can be transmitted from the rear differential via the cross-member and into the passenger compartment. To minimise this effect, they developed three large rubber bearings that effectively decouple the rear differential.
Air suspension: substantially enhanced comfort and dynamics
As in the case of the front axle, the steering and the rear axle, Mercedes-Benz also made further improvements to the air suspension system that comes as standard in the S Class. The focus was on finding the technical means to reconcile the con-flicting objectives of superb driving comfort and excellent handling dynamics. This involved completely reworking the AIRMATIC system.
The system of the predecessor model already set standards in regard to comfort, but the new S Class once more raises the bar in this area. The Mercedes engineers accomplished this by improving a number of details:
- The air spring struts are now made with separate paths for the transmission of the damping and cushioning forces at the head. This made it possible to tune the bearings in the way best suited to their separate tasks. For example, the head bearings for the shock absorbers are tuned for a soft damping in or-der to follow the front-axle movements along the entire spring travel distance without transmitting comfort-reducing lateral forces into the spring strut.
- The engineers at Mercedes have also improved the air springs’ rubber bellows, which keep the compressed air in the spring struts. Their wall thickness has been reduced by 0.2 millimetres to just 1.5 millimetres. As a result, it now offers even better ride comfort and it responds with high sensitivity to even small influences when driving on bumpy roads.
- Friction was also the top issue addressed during the enhancement of the gas shocks. The solutions developed by the experts at Mercedes include new, pressure-reducing valves, single-lip seals for the shock absorber shafts and an ultra-low-friction Teflon strip surrounding the working pistons of the shock absorbers.
Degressive damper characteristics for agile handling
Do you desire a comfortable or a more dynamic ride? In the new S Class, this question is easily answered, as the enhanced air spring system sets standards for both types of ride. This is because Mercedes-Benz combines the air springs with the Adaptive Damping System (ADS) as standard. ADS constantly regulates the shock absorber force in line with requirements, taking the road conditions, the driving style and the car’s load into account. Under normal driving conditions, the system puts the dampers on a soft setting. However, when driving becomes more dynamic, for example when the car has to suddenly evade an obstacle or when braking, the system can respond within 50 milliseconds to adjust the damping force at each wheel. In doing so, the skyhook algorithm regulates the damping forces in such a way that the forces exerted on the car body by the movement of the wheels is reduced. Depending on the steering commands, the ADS solenoid valves can set the shock absorbers to four different stages:
- Stage 1: Soft bump and rebound for a comfortable ride with minor build-up motion and low acceleration values.
- Stage 2: Skyhook mode - soft rebound setting and hard bump stage.
- Stage 3: Skyhook mode - soft bump setting and hard rebound stage.
- Stage 4: Hard bump and rebound setting to reduce wheel load fluctuations during dynamic driving.
When experiencing few body movements during a drive, the new S Class uses the comfortable ADS Stage 1. If the build-up speed exceeds a certain value, the sys-tem shifts to the skyhook algorithm and continuously switches between the sec-ond and third damping stages with the help of fast solenoid valves in order to off-set body roll and pitching.
In the new S Class, Mercedes-Benz has further improved the effectiveness of the Adaptive Damping System by developing degressive shock absorber characteris-tics. These permit an even larger spread of damping forces between the shock ab-sorber’s bump and rebound stages, thus contributing greatly to the saloon’s agile handling properties. As a result, the damping effect of the degressive pistons in-creases more strongly when the dynamic driving stimulation is low (when faced with quick steering movements, for example) than is the case with the previous linear characteristics.
The system takes the road conditions into account when regulating the shock ab-sorbers as required by the situation. Thanks to an improved computing process (algorithm), the system can recognise the prevailing road conditions with greater precision than was previously the case.
Individualised chassis and transmission characteristics at the push of a button
Another special feature of the new S Class is the S/C/M button in the centre con-sole. The motorist can use this button to switch the saloon’s characteristics from “ comfortable” to “sporty” and individually set the vehicle’s chassis, height and transmission program:
- Comfort: When the speed exceeds 120 km/h, AIRMATIC automatically low-ers the body by ten millimetres at both axles in order to improve driving sta-bility and reduce drag. When the velocity exceeds 160 km/h, the body is low-ered by further ten millimetres and the bump stage damping is changed to “hard”. When the speed again drops below 80 km/h, the system returns the body to its normal height. The automatic transmission shifts gears at low en-gine speeds and allows the S Class to begin driving when in second gear.
- Sport: The body is lowered by 20 millimetres at both axles when the speed reaches 100 km/h and is not raised again until the velocity drops below 60 km/h. The shock absorbers are set to the “hard” bump stage from 40 km/h. When changing gears, the automatic transmission exploits the engine’s full rpm range.
- Manual: The automatic transmission can be operated manually by means of buttons on the steering wheel. Body height and chassis are set as in the “Sport” mode.
When the S Class is travelling on poor roads that require greater ground clear-ance, the driver can raise the vehicle’s body by 30 millimetres at the press of a button.
Active Body Control: Perfect combination of dynamism and comfort
With the introduction of Active Body Control (ABC) in 1999, Mercedes-Benz reor-ganised the alphabet of chassis technology. The innovative system, which entered series production after 20 years of research and development, is the solution to the traditional problem associated with the tuning of a passenger car chassis: Should the road vibrations on the wheels be kept to a minimum by setting the shock absorbers to a sporty stiff mode, or should the damping be kept as soft and comfortable as possible at the expensive of driving safety and dynamic handling? Thanks to Active Body Control, there is no longer any need to choose between these conflicting objectives, as the chassis setting will automatically be adjusted to the prevailing driving situation. As a result, a high level of comfort will be at-tained even with dynamic handling and vice versa.
In Mercedes-Benz’ active chassis system, the four spring struts are equipped with microprocessor-controlled plunger cylinders that can almost completely compen-sate for lifting, rolling and pitching of the body. The computer uses various accel-eration sensors to obtain information on the current driving situation and com-pares this 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 that the servo-hydraulic valves at the front and rear axle transform into precisely metered flows of oil.
If oil flows into the plunger cylinder, the valves adjust the base positions of the steel springs integrated into the spring struts. In this way they create the forces needed to counteract the body movements. Because of the continuously available hydraulic pressure of up to 200 bar, the ABC can spontaneously stabilise the body within a fraction of a second. The system operates in the vibration range extend-ing up to five Hertz, which makes itself felt on rough road surfaces as lifting and rolling movements, in curves as a pronounced roll, and as the typical pitching of the body when braking. Passive double-tube gas shock absorbers are responsible for the higher-frequency vibrations.
Rolling tendency when cornering at speed reduced by 60 per cent
Mercedes-Benz has made further improvements to the active chassis system (standard equipment in the S 600) for the new S Class. Each component has been reworked. The experts have combined various components in order to reduce the amount of space the system requires and improve the control functions by means of shorter cable connections.
The essential advantage of second-generation Active Body Control, however, is its further improved performance in reducing body movements to correspond to in-dividual driving situations. This is where the S Class advances into new dimen-sions of driving dynamics - while simultaneously offering greater comfort that every driver will immediately notice. The body’s roll angle, for example, is reduced during a dynamic driving manoeuvre by more than 60 per cent — from the previous value of 3.1 to 1.2 degrees. When driving through curves at higher speeds — for example on a motorway exit — the second generation ABC chassis reduces the roll angle to only 0.75 degrees. That is also more than 60 per cent less than the value for the predecessor model of the new S Class.
Other notable features of Active Body Control are the variable roll moment distri-bution between the front and rear axles, which the system carries out automati-cally according to the speed, and the load adjustment system. At speeds of be-tween 65 and 140 km/h, ABC automatically lowers the body by as much as 15 millimetres to reduce wind resistance. If more ground clearance is needed when driving on poor road surfaces, the driver can raise the level of the vehicle by 40 millimetres by simply pressing a button. The “S/C/M” selector button is also in-cluded in Active Body Control for the S Class and makes it possible to adjust the chassis and transmission characteristics to individual needs.
Braking system: high-tech for greater safety and comfort
ADAPTIVE BRAKE - the name of the S Class braking system alone is a clear indi-cator that still another new development is going into series production. The hy-draulic dual-circuit braking system is electronically controlled, which makes possible driver-assistance functions that boost safety and comfort:
- HOLD: After the saloon has been braked to a full stop, the driver only has to briefly depress the brake pedal a bit further to activate this function. The S Class is then held in place by the brake — even if the driver takes his or her foot off the brake pedal. This is how the HOLD function prevents unintended forward rolling at traffic lights, stop signs or in stop-and-go traffic. When the vehicle is once again driven forward, the hold function is automatically deactivated.
- Hill holder: With this added function, ADAPTIVE BRAKE prevents the S Class from rolling backwards when a driver’s foot is moving from the brake to the gas pedal while starting out on an uphill incline. If the sensor technol-ogy detects that the saloon has stopped on an incline, the hill holder automati-cally turns on and briefly maintains constant pressure on the brake to make starting out easier.
- Advance braking pressure: If the driver suddenly removes his foot from the gas pedal, the braking system recognizes an emergency braking situation. In such instances, ADAPTIVE BRAKE increases the pressure in the brake lines and brings the pads into contact with the brake discs, so that they can grip in-stantly with full force when the brake pedal is pressed. With this function, the system supports Brake Assist or Brake Assist PLUS.
- Brake-drying: In vehicles being driven on wet roads, ADAPTIVE BRAKE uses brief braking impulses at regular intervals to ensure the film of water on the brake discs is removed and the brakes will have their full stopping power when needed. This automatic brake-drying function is activated when the windscreen wipers have been in operation for a certain time. The driver does not notice the finely metered braking impulses.
Large brake discs on the front and rear axles provide the technological basis for safe and reliable deceleration using ADAPTIVE BRAKE. Depending on the engine installed, the disc diameters range up to 360 mm in the front and up to 330 mm in the rear. The front brake discs are perforated for all models. 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. The new Mercedes-Benz S Class braking system at a glance:
|Front axle||S 350, S 320 CDI||S 500||S 600|
|Brake calliper |
|4-piston solid calliper |
2 x 77 cm²
|4-piston solid calliper |
2 x 77 cm²
Internally ventilated, perforated
|8-piston solid calliper |
4 x 54 cm²
Internally ventilated, perforated
|Brake calliper |
|1-piston solid calliper |
2 x 38 cm²
|1-piston solid calliper |
2 x 38 cm²
|4-piston solid calliper |
2 x 48 cm²
Safety systems: new functions increase efficiency
ABS, ASR, ESP®, Brake Assist — the tried and tested safety systems developed by Mercedes-Benz are part of the standard equipment in the new S Class and offer additional new functions.
For example, the Mercedes engineers have equipped the anti-lock braking system (ABS) with additional technology that makes braking on surfaces that are slip-pery on only one side of the vehicle even safer. The system can recognise such situations and controls the braking pressure in such a way that the driver is given the best possible support with regard to steering stability. The ABS in the new S Class also offers enhanced safety when braking on bends by distributing the braking force as required, thus producing a yawing moment that counteracts the vehicle’s yaw and stabilises it. The braking system uses the data supplied by the ESP® sensors in order to identify such situations reliably.
The Electronic Stability Program also improves the ASR acceleration skid control system: ESP® sensors provide online information about the respective tyre skid-ding and allow the traction control system to be more precisely activated, which leads to significant improvements, especially when driving along slippery roads. Another ASR function is the “snow chain logic,” which automatically detects that snow chains are mounted on the basis of the tractive force and travelling resis-tance and adjusts the acceleration skid control accordingly.
When driving quickly around a curve, a new yawing moment control first records the stiffness of the respective tyre and thus improves the ESP® control when the S Class is fitted with winter tyres. The new, electronically controlled brake system ADAPTIVE BRAKE offers additional advantages, since the electronics selectively control the brake booster, which means that the ESP® can work comfortably and with high sensitivity. Furthermore, the system is quicker and more effective than before: The ESP® automatically reduces the distance between the brake lining and brake disk when there is danger of skidding and the S Class has to be stabilised through targeted braking impulses.
An extra function incorporated into the Electronic Stability Program offers drivers even greater safety when towing a trailer. The new ESP® trailer stabilisation sys-tem detects if the trailer is swaying dangerously and automatically stabilises it by applying targeted braking impulses to the wheels of the towing car.
On request, Mercedes-Benz will equip the new S Class with a swivel-mounted tow-bar, the tow ball of which has to be neither mounted nor removed. It swivels below the body together with the socket and is not visible in the reclining posi-tion. This top-of-the-range Mercedes model has a maximum towing capacity of 2,100 kilograms.
Parking brake: comfortable with an electric motor
The new S Class features an extremely easy-to-use electric parking brake as stan-dard. A push of 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 re-leased. The key components of this new development are two separate servo drum brakes on the rear wheels and an electric motor with speed-reducing gear that applies the brake clips by means of cables. The electric parking brake can also be locked if the engine is switched off.
Wheels and tyres: a choice of eight different combinations
Appealing alloy wheels are standard equipment in the new S Class. The saloons with V6 engines are fitted with 17-inch seven-spoke wheels. Mercedes-Benz has developed a five-spoke design for the eight-cylinder S 500, and the top-of-the-line S 600 will be launched on the market in 2006 with 18-inch five-spoke forged wheels.
Thanks to the extensive range of wheels and tyres, Mercedes customers have plenty of choice when it comes to equipping their S Class to meet their own tastes. An overview of the standard and optional equipment:
- 8 J x 17, 235/55 R 17 (standard in the S 350 and S 320 CDI)
- 8 J x 17, 235/55 R 17 (standard in the S 500)
- 8.5 J x 18, 255/45 R 18
- 8.5 J x 18, 255/45 R 18 at the front; 275/45 R 18 at the rear (standard in the S 600)
- 8.5 J x 18, 255/45 R 18
- 8.5 J x 18, 255/45 R 18 at the front; 9.5 J x 18, 275/45 R 18 at the rear
- 8.5 J x 19, 255/40 R 19 at the front; 9.5 J x 19, 275/45 R 19 at the rear
AMG five-spoke design, polished:
- 8.5 J x 19, 255/40 R 19 at the front; 9.5 J x 19, 275/40 R 19
In order to stay mobile in the event of a flat tyre, Mercedes-Benz offers tyres with run-flat properties as an option. These tyres feature self-supporting side walls. This means that Mercedes customers can continue driving for up to 100 km at a top speed of 80 km/h despite having a flat tyre.
Tyre pressure loss warning system, standard
The tyre pressure is monitored by the ESP® Electronic Stability Program or, on request, a special control system based on wireless 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 transverse acceleration, yaw rate and wheel torque, in order to determine loss of pressure in a tyre. In doing so, the system detects any deviations and in-forms the driver via a message on the central display panel: “Tyre pressure, check tyres”. The tyre pressure lost warning system based on ESP® technology is part of the standard equipment in the S Class.
- In the tyre pressure control system (optional), a sensor measures both the air pressure and the air temperature inside the tyre and transmits the data by radio to a receiving antenna attached to the underbody at regular intervals. On the basis of intelligent software, the wheel positions are automatically local-ised so that the driver has access to specific information about the air pressure on each of the four tyres via the central display panel.