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The new Mercedes-AMG SL: the chassis
The SL 55 4MATIC + is equipped as standard with a newly developed AMG RIDE CONTROL steel spring chassis with particularly light and powerful aluminum shock absorbers including adjustable damping and lightweight coil springs. For the first time, a series-production vehicle from Mercedes-AMG has a multi-link front axle with five links that are arranged completely within the rim. This significantly improves the kinematics. The independent wheel guidance and suspension elements enable high lateral accelerations with minimal drive influences on the steering system. A 5-link space structure also guides the wheels on the rear axle. The innovative AMG ACTIVE RIDE CONTROL suspension with active, hydraulic roll stabilization also celebrates its premiere in the SL 63 4MATIC +. The system enables even better steering and load change behavior with typical AMG dynamics, precision and feedback for the driver. At the same time, it increases driving comfort when driving straight ahead and when driving over bumps.
In order to reduce the unsprung masses, all suspension arms, steering knuckles and wheel carriers on the front and rear axles of the new SL are made of forged aluminum. The multi-link concept guides each wheel with the slightest elastic movement. The high camber and track stiffness not only enable high cornering speeds, it also gives the driver optimum contact with the road in the cornering border area located high up. This is evident in the excellent lateral dynamics and driving stability at high speeds as well as in the good-natured reaction to external influences such as cross winds, bumps or jumps in the coefficient of friction. A particularly direct connection of the shock absorber to the rear wheel carrier reduces vibrations and unwanted wheel load fluctuations. The independent wheel guidance and suspension elements enable high lateral accelerations with minimal drive influences on the steering system - also a comfort feature.
The lightweight coil springs are a new development: Thanks to a special heat treatment, their weight could be reduced without reducing performance. In the manufacturing process, the spring pad is glued to the spring for the first time. This fixed connection prevents wear and tear from ingress of dirt such as sand over the course of the vehicle's life. The spring does not corrode over its life cycle and the maximum component load can consequently be increased with a lower weight. This saves around 0,2 kilograms per spring.
Another lightweight construction measure concerns the torsion bar stabilizers on the front and rear axles in vehicles without active roll stabilization. Thanks to a variable wall thickness, their weight can be reduced. For this purpose, the raw material is tailored to the load in the vehicle using a special drawing process. The maximum wall thickness is only used where it is required due to the maximum load, in this case in the area of the rubber mounts.
Even more comfort and sportiness: adaptive adjustable damping with two valves
The SL 55 4MATIC + has the latest generation of AMG adjustable damping as standard. This system works with two so-called pressure relief valves per damper. With the help of these stepless control valves, a significantly larger damping force spread can be achieved: One valve controls the rebound stage, i.e. the force that is created when the wheel rebounds, and the other the compression stage when the wheel compresses. The rebound and compression levels are regulated independently of each other. In detail, this means that the so-called soft characteristic curve of the shock absorber has been reduced and the hard characteristic curve of the shock absorber has become even more pronounced. The structure cushions more sensitively in the event of bumps and decouples entries from the road. At the same time, the further refined control of the rebound valve and compression valve (stepless and independent of each other) stabilizes the structure as well as possible. This technology makes it possible on the one hand to increase comfort, but on the other hand to make the driving dynamics even sportier.
The chassis control unit uses data analysis - including from acceleration and wheel travel sensors - to adjust the damping force for each wheel in a matter of milliseconds, depending on the situation. By using the two adjusting valves, the damper is able to guarantee the damping force adjustment in all areas of the wheel vibrations. Due to the special design of the valves, the damper reacts quickly and sensitively to changes in road surfaces and driving conditions.
The driver can pre-select the basic set-up using the AMG DYNAMIC SELECT drive programs: At the push of a button, the driving behavior changes, for example, from full dynamism in the “Sport +” mode to smooth gliding in the “Comfort” setting. In addition, the tuning can be adjusted in three stages via its own button, independently of the driving programs.
For the first time in series: AMG ACTIVE RIDE CONTROL with hydraulic, active roll stabilization
A completely newly developed hydraulic system is used in the SL 63 4MATIC + that is going into series production for the first time in a Mercedes-AMG model: the innovative AMG ACTIVE RIDE CONTROL suspension. Biggest innovation: Active hydraulic elements replace the conventional mechanical torsion bar anti-roll bars and compensate for rolling movements of the new SL in fractions of a second. The adaptive shock absorbers also have two hydraulic connections. One of them is on the compression side of the damper, the other on the tension side. The connection of the damper chambers on all four wheels and the lines takes place directly via the control valves of the adaptive dampers.
The intelligent hydraulic interconnection of the four struts and the pressure regulation of the pump and switching valves allow a very wide roll spring rate with simultaneously reduced roll movements. Figuratively speaking: every torsion bar from zero to rigid can be displayed automatically. In everyday life, this increases comfort because even uneven spots are individually compensated for. When cornering dynamically, the hydraulics also actively reduce the loss of falls. Thanks to the resulting high camber stiffness, the roadster turns very precisely.
When driving straight ahead, the system opens completely, depending on the driving program and driving situation. The system shuttles out individual obstacles that would otherwise lead to rolling movements. Driver and passengers experience a much more comfortable driving experience. The reduced rolling movements when cornering contribute equally to comfort and driving dynamics. The characteristics of the driving behavior in the individual driving programs can also be spread even more between comfort and sport.
All dampers are hydraulically connected to each other
The basic principle of the chassis is based on the fact that the push or pull sides of the individual dampers of the vehicle are interconnected. The compression stage of the front left damper is connected to the rebound stage of the front right damper via a hydraulic line. In addition, a line across the vehicle also connects to the pressure side of the rear left damper and the rebound stage of the rear right damper. Analogously to this, the other sides of the damper chambers are connected to one another via a second circuit. The simplified courses of the hydraulic lines each result in the shape of an "H".
In addition to the interconnection of the dampers, other components that are important for the function are used in the system. The push and pull sides of the dampers are directly connected to each other via an electrically controllable 2/2-way valve, called a comfort valve. A pressure accumulator is also attached to each of the damper pressure sides. Both circuits are also connected to a central pump. It ensures that the hydraulic system pressure can be set in both circuits. The connection between the pump and the circuits is made via 2/2-way valves. Pressure sensors are integrated behind the valves to monitor the system pressure in the respective lines. The system pressure can be freely selected and thus also the size of the generated roll support. The following applies: the higher the system pressure, the greater the expected roll stiffness.
The system works very efficiently because it uses the existing kinetic energy of the vehicle to positively influence the rolling behavior. The hydraulics of the AMG ACTIVE RIDE CONTROL suspension also feeds the optional lift system for the front axle. If necessary, the front end is raised by 30 millimeters and makes it easier, for example, to enter underground garages or drive over thresholds. The lift system is operated via the multimedia central display or the AMG steering wheel buttons. The corresponding menu opens after pressing the area with the vehicle symbol on the control bar. Among other things, positions can be saved using GPS technology so that the vehicle in front of the car is automatically lifted when it passes the corresponding points again.
Rear axle locking differential for optimized driving stability
The SL 63 4MATIC + has an electronically controlled rear-axle limited-slip differential as standard, which guarantees excellent traction and maximum driving safety in all driving conditions. For the SL 55 4MATIC + it is available as part of the optional AMG DYNAMIC PLUS package. Not only is the traction of the drive wheels on the rear axle further improved. The cornering speeds in the limit area also increase. In addition, driving stability is optimized when changing lanes at high speed. The system works with a variable locking effect in pulling and pushing operation and is perfectly matched to the different driving conditions and road surface friction values.
AMG high-performance composite braking system for short braking distances
The newly developed AMG high-performance composite brake system guarantees excellent deceleration values and precise control. It impresses with short braking distances, sensitive responsiveness and, last but not least, with high stability and service life - even under extreme loads. The comfort functions include hill start assist, priming and braking when wet. When the ignition is switched off and the vehicle is stationary, the gearbox also automatically activates the "P" parking position; the electric parking brake is automatically released when the vehicle starts moving.
The composite brake discs are particularly light: Driving dynamics and steering behavior benefit from the reduced unsprung masses. Brake disc (made of cast steel) and brake pot (made of aluminum) are now connected with special pins and no longer with screws as before. This construction saves space that is used for even better brake cooling. The directional perforation is also new: in addition to weight savings and better heat dissipation, this solution scores with faster response in wet conditions and better pad cleaning after braking.
On the two SL variants with V8 engines, internally ventilated and perforated composite brake discs measuring 390 x 36 millimeters with 6-piston fixed calipers are mounted at the front, and on the rear axle measuring 360 x 26 millimeters with 1-piston floating calipers. The SL 55 4MATIC + has brake callipers painted red, the SL 63 4MATIC + has yellow.
On request, both SL variants can be equipped with the AMG ceramic high-performance composite brake system, with brake discs measuring 402 x 39 millimeters on the front axle and 360 x 32 millimeters on the rear axle. Compared to the standard brake, it saves even more weight. At the same time, the ceramic discs withstand even extreme loads and keep braking distances short - ideal for use on the racetrack, for example. Thanks to the bronze paintwork of the brake calipers, they are also instantly recognizable as absolute high-performance components. All coverings are copper-free and therefore more environmentally friendly.
