AMG sports suspension and high-performance braking system: New standard in driving dynamics thanks to Direct-Steer system, Torque Vectoring Brake and Active Body Control with crosswind stabilisation

Jun 22, 2009
The AMG sports suspension and ADAPTIVE BRAKE high-performance braking system are every bit a match for the effortlessly superior drive units: the two top-of-the-line models, the S 63 AMG and S 65 AMG, raise the bar in terms of driving dynamics thanks to new high-tech systems.
Less steering effort, more agile handling with the same outstanding straight-line stability – the new Direct-Steer system in a nutshell, which is now fitted as standard on the S 63 AMG and S 65 AMG. A key feature of the Direct-Steer system is the variable-ratio steering rack that operates using purely mechanical means. While the power steering around the central position utilises an indirect ratio to promote excellent straight-line stability, this alters from a steering angle of around five degrees: really small steering angles are all it takes to perform precise cornering, noticeably improving handling on winding country roads. The steering angle requirements have also been modified, enabling the driver to steer the AMGsaloons far more easily, particularly on urban roads. Compared with a steering system with a constant ratio, the number of revolutions from lock to lock is reduced by around 25 percent with the Direct-Steer system.
Purely mechanical Direct-Steer system with a host of benefits
Another advantage of the purely mechanical Direct-Steer system is the absence of any elaborate actuators and complex sensors – with associated benefits in terms of weight, installation space and susceptibility to faults. The constant steering response is also advantageous compared with other variable steering systems that sometimes require the driver to adapt quickly to what are fast changing situations on the road.
The Direct-Steer system is based on the familiar speed-sensitive power steering system which reduces the power assistance as the road speed increases. Easy manoeuvrability on urban roads where large steering angles and thus a great deal of power assistance is required, is coupled with reduced support at high speeds, say on the motorway – all of which improves straight-line stability and handling safety.
Torque Vectoring Brake optimises driving dynamics and handling safety
A further improvement in driving dynamics as well as active handling safety comes courtesy of the new Torque Vectoring Brake. If the Electronic Stability Program ESP®detects the onset of understeer, short one-sided braking intervention on the vehicle's inside rear wheel generates a specific yawing moment around the vehicle's vertical axis within a fraction of a second. Consequently, the AMG S-Class handles precisely and remains under control at all times as well as also bolstering active handling safety by reducing the tendency to understeer. The Torque Vectoring Brake is standard on the S 63 AMG and S 65 AMG.
Crosswind stabilisation as new Active Body Control function
The AMGsports suspension now comes as standard with automatic crosswind stabilisation based on Active Body Control (ABC). The ABC control electronics
vary the wheel load distribution so that the effect of crosswinds is virtually compensated or reduced to a minimum. If the S-Class is affected by a crosswind, the ABC control unit utilises the yaw-rate, lateral acceleration, steering angle and speed sensors of the Electronic Stability Program ESP® to trigger diagonal wheel load distribution instantly – for instance on the left front and right rear wheel. The associated steering effect reduces the effect of the crosswind. Crosswind stabilisation is activated at speeds above 80 km/h while travelling in a straight line or on slight bends. The function is deactivated if the driver himself makes heavy, brusque steering corrections.
The active suspension on the S 63 AMG and S 65 AMGall but entirely eliminates the body movements that occur when moving off, cornering and braking. Bends are negotiated with far less roll; the body roll caused by fast evasive manoeuvring is effectively suppressed. Other notable features of Active Body Control are the variable roll moment distribution between the front and rear axles, which the system carries out automatically according to the speed. The computer uses various acceleration sensors to obtain information on the current driving situation and compares 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.
The load adjustment system enables the current vehicle weight to be factored into the calculation processes for the active suspension. As such the S 63 AMGand S 65 AMG handle just as dynamically even when the car is fully laden. Briefly pressing the Sport button next to the AMG instrument cluster changes the characteristics of the AMGsports suspension: the roll angle through fast corners is reduced further, the shock absorbers and springs also respond firmer to promote agility. At speeds of between 65 and 100 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 at a speed up to 30 km/h by simply pressing a button.
AMG high-performance braking system based on ADAPTIVE BRAKE
Based on the ADAPTIVE BRAKE system, the AMGhigh-performance braking system continues to set the benchmark for stopping power, sensitivity and fade resistance. The front axle features a double floating brake calliper; this technology combines the advantages of a sliding-calliper disc brake – reduced heat transfer to the brake fluid and clear advantages in terms of comfort thanks to the brake lining guide mechanism – with the efficiency of an extra large fixed calliper brake. At the rear, braking is handled by a large sliding frame-type calliper. Internally ventilated, perforated composite brake discs at the front and rear with a diameter of 390 and 365 millimetres respectively ensure the shortest stopping distances, remarkable resistance to fading and outstanding sensitivity.
The hydraulic dual-circuit braking system is controlled electronically, permitting the inclusion of numerous driver assistance functions that improve safety and comfort – such as "priming" the braking system in critical situations: if the driver suddenly switches from the accelerator to the brake pedal before emergency braking, ADAPTIVE BRAKE increases the pressure in the brake lines and applies the pads to the brake discs, so that they can grip instantly with full force when the brake pedal is pressed. In wet weather, the system injects regular, short brake impulses to ensure that the film of water on the brake discs is wiped off and the brakes can work as effectively as possible. This automatic brake-drying function is always activated when the windscreen wipers on the S-Class have been in operation for a certain time; the driver does not notice the finely metered braking impulses.
After the S-Class 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 car 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.
Eye-catching light-alloy wheels in 19 and 20-inch format
High-sheen 19-inch AMGfour-spoke light-alloy wheels painted titanium grey provide the contact between the road and the S 63 AMG. 255/40 R 19 tyres are fitted on 8.5-inch-wide wheels at the front, while 275/40 R 19 tyres combine with 9.5-inch-wide wheels at the rear. The S 65 AMG comes with 20-inch AMG twin-spoke forged wheels, painted in titanium grey with a mirror finish, measuring 8.5 and 9.5 inches wide. 255/35 R 20 tyres are fitted at the front, while 275/35 R 20 tyres feature at the rear.