The new Mercedes-Benz S-Class: Suspension - The world's first suspension system with "eyes"
The front axle features four-link suspension. Its key characteristics include two individual links (torque strut and spring link) in the lower link plane. The transversely situated forged-aluminium spring link carries the spring strut. The anti-roll bar is connected directly on the steering knuckle, while the forward-sloping torque strut is made of forged aluminium.
A wishbone located high above the lower link plane performs further wheel location functions. This link is also made of forged aluminium, as is the steering knuckle which connects the upper and lower link planes. The fourth link is the track rod which forms part of the rack-and-pinion steering system. The transversely situated steering gear is located in front of the wheel's centre.
The arrangement and design of the wheel location components offer favourable characteristics for the axle kinematics: the kingpin inclination is close to the wheel centre. This provides for large longitudinal force leverage, thus minimising sensitivity to tyre imbalances and fluctuations in braking force.
The lower front axle components, the steering gear and the engine mounts are linked with an assembly carrier. This integral carrier, made from high-strength sheet aluminium, is directly bolted to the body.
Due to the unsurpassed wheel location qualities, the S-Class features multi-link rear suspension attached to a subframe. Consistent lightweight construction minimises the weight of the unsprung masses. Four of the five wheel-locating links are made of forged aluminium, as is the hub carrier. The spring link that carries the spring strut is made of single-ply sheet aluminium. In the standard configuration, the rear axle with air suspension features a torsion-bar stabiliser which is directly connected to the rear axle carrier.
AIRMATIC: enhanced comfort and driving dynamics
The standard-fit full air suspension system AIRMATIC with continuously adaptive damping control allows the spring travel to be maintained whatever the vehicle load by means of continuous level adjustment. The vehicle level is controlled automatically depending on the vehicle speed. It is lowered by up to 20 millimetres when the speed exceeds 120 km/h. Consequently, aerodynamic drag is lowered and, thanks to the low vehicle centre of gravity, directional stability is enhanced.
The AIRMATIC system with continuously adaptive damping control that featured on the predecessor model has been modified in many respects: new air suspension bellows with reduced breakaway torque make for even better ride comfort as they do not stiffen as much at low amplitudes and larger frequencies. The spring travel on the rear axle has been increased, thus improving absorption capacity if excitation is high. To further reduce tyre noise, the air suspension struts on the rear axle are decoupled from the body.
The lower control panel on the centre console allows the driver to raise the vehicle level by 30 millimetres on poor road surfaces or when confronted by a tricky garage entrance, for example.
Further improvements have likewise been made to the adaptive damping system. This fully automatic, electronically controlled system adjusts the shock absorbers on each wheel as required. As before, the single-tube shock absorbers are equipped with a valve each for the compression and rebound stage, while there is a new feature in the shape of continuous damping adjustment. This means that the optimum operating point can be selected every time based on various data such as acceleration, vehicle level or vehicle speed. A button on the centre console allows the driver to select a sportier setting as an alternative to the comfort-oriented default setting.
If certain vehicle speed thresholds are exceeded or not reached, the normal vehicle level is restored automatically.
MAGIC BODY CONTROL: the world's first suspension system with "eyes"
The new S-Class is the world's first car to be able to detect bumps on the road ahead. The MAGIC BODY CONTROL suspension system available as an option for the eight-cylinder models includes ACTIVE BODY CONTROL (ABC) and the new and innovative ROAD SURFACE SCAN function.
The "eyes" for the ROAD SURFACE SCAN function are provided by a stereo camera fitted behind the windscreen, which scans the road up to 15 metres ahead of the vehicle and delivers a precise image of the road contours. Based on the camera pictures and driving status information, the control unit constantly calculates the best control strategy for overcoming unevenness such as prolonged bumps.
The vehicle can therefore adjust the damping of each individual wheel to a tauter or softer setting in advance and increase or reduce the load on the wheel by means of an active hydraulic system. The suspension is adapted to a given situation within fractions of a second, and body movement can be reduced considerably. This results in a hitherto unprecedented level of ride comfort. Because ROAD SURFACE SCAN is camera-based, it can work throughout the day if visibility is good, the road structure is suitable and even at speeds of up to 130 km/h.
In the Active Body Control system from Mercedes-Benz, the four spring struts are equipped with hydraulic cylinders (plungers) to adjust the force in each spring strut individually. This means that the system can almost completely compensate for lifting, rolling and pitching of the body. The control unit receives information on the current driving situation from various acceleration sensors and then 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 for the servo-hydraulic valves at the front and rear axle to ensure 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. Thanks to a constantly available hydraulic pressure of up to 200 bar, ABC is able to stabilise the body within fractions of a second.
The ABC has undergone major modifications for the new S-Class: the wheel damping is now continuously adjustable, the spring strut response has been improved and the pump efficiency has been further enhanced. A digital interface connects the control unit and the sensors, while the fast FlexRay bus connects the control unit and the vehicle electronics. Processing power is more than double that of the previous system.
Steering: electro-mechanical Direct-Steer system and steering assistance
The new S-Class comes with an electro-mechanical Direct-Steer system as standard. As well as a more precise and also more comfortable steering experience, the steering system has a major impact on overall efficiency, since it only requires energy when the vehicle is actually being steered.
In the new steering system, the steering gear and the supporting servo-motor form a single compact unit and are mounted on an extremely rigid and low-weight integral support frame made of aluminium which is positioned in front of the wheel's centre line. The steering gear is designed as a Direct-Steer system, which means that the steering ratio becomes noticeably more direct over the steering angle. This enhances the vehicle's handling and agility substantially.
The steering assistance function can help to stabilise the vehicle. An assistance steering wheel torque is determined depending on the driving conditions, and this is set accordingly by the electric steering assistance.
The function never overrules the driver but, instead, indicates the direction in which to steer to stabilise the vehicle. In the event of oversteer, the steering assistance system prompts the driver to countersteer via the steering wheel until the vehicle has stabilised again.
If the vehicle is braked on a road surface with different friction (µ-split) on the left and right, there is a yaw impulse which turns the vehicle in the direction of the high friction. The steering assistance system prompts the driver to turn the steering wheel in the appropriate direction to compensate for the yaw caused by the different friction.
Brakes: large discs, a wealth of assistance functions
Large brake discs at the front and rear provide the technological basis for safe and reliable deceleration using the ADAPTIVE BRAKE electronic brake control system. Depending on the engine installed, the disc diameters are up to 370 millimetres at the front and up to 360 millimetres at the rear. The S-Class features an electric parking brake as standard. A combined floating calliper with electric parking brake function is used on the rear axle.
With the ADAPTIVE BRAKE, the S-Class offers a wealth of assistance functions. One example of this is the practical HOLD function: after braking to a standstill, briefly pressing the brake pedal a little further is all that is required to activate this function. The car is then held by the brakes, even if the driver's foot comes off the brake pedal. The HOLD function is deactivated automatically when the car moves off.
If the driver's foot moves abruptly from the accelerator to the brake pedal before an emergency stop, the brake system increases the pressure in the brake lines and brings the pads into contact with the brake discs so that maximum braking power is available as soon as the driver hits the brake pedal. This priming of the brakes allows the system to assist the standard-fit Brake Assist system.
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. The finely metered brake pulses are imperceptible to the driver. This automatic brake drying function is always activated when the windscreen wipers have been operating for a certain length of time.
Finally, ADAPTIVE BRAKE assists the driver when starting on an uphill slope. When the sensors detect that the Saloon has stopped on an uphill slope, Hill Start Assist is activated automatically, briefly holding the brake pressure at a constant level so as to prevent the car from rolling backwards.
The ESP® Dynamic Cornering Assist offers improved safety in critical cornering conditions. If the ESP® sensors detect an understeering tendency, the ESP® performs specific braking intervention on the side of the vehicle which is on the inside of the bend. This gives rise to gentle rotary movement of the vehicle around the vertical axis.
Crosswind Assist: strong gusts no longer a scare
Crosswind Assist helps the driver as it can substantially reduce the effect strong crosswinds have on the vehicle's straight-line stability.
In vehicles without ABC, the negative effect of the crosswind is compensated for by braking on one side of the vehicle activated by ESP® in the ADAPTIVE BRAKE, which is already being used by the Active Lane Keeping Assist/Blind Spot Assist. In vehicles with ABC suspension, crosswind stabilisation is achieved by means of targeted wheel load changes by adjusting the ABC dampers.
Credits: Daimler AG
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