The chassis and suspension: Excellent dynamics without compromising on comfort

Sep 18, 2012
Supreme driving dynamics coupled with superlative ride comfort on long journeys were the terms of reference in developing the chassis for the new CLS Shooting Brake, whose design and functions are geared towards a stylish sportiness.
As on the CLS Coupé, the front suspension takes the form of a 3-link front axle with McPherson struts. The key feature of this modified suspension is two individual links (pulling strut and cross strut) in the lower link plane. The stabiliser is connected to the suspension strut. The forward-sloping pulling strut is designed as a weight-optimised forged aluminium component, while the cross strut fitted in lateral direction is a weight-optimised forged steel component. The tie rod is defined as the third link, forming part of the rack-and-pinion steering system. The arrangement and design of the wheel control parts, and in particular the manner in which the lower A-arm is divided into two individual links, offer more favourable characteristics for the axle kinematics than the fixed A-arm. The kingpin inclination is closer to the wheel centre. This provides for large longitudinal force leverage, thus minimising sensitivity to tyre imbalances and fluctuations in braking force.
The principle of the lightweight multi-link independent rear suspension has been adopted for the CLS Shooting Brake from the E-Class Estate on account of its unsurpassed wheel control qualities. As on the E-Class Estate, the front cross-bar of the axle housing is supported by the vehicle body over a wide area. This reduces the forces transmitted into the passenger compartment, a comfort feature that is particularly noticeable when crossing transverse joints in the road surface. In keeping with the lightweight-design concept at the heart of the new CLS Shooting Brake, wheel location components such as struts, hub carriers and the metal sections of the
elastomer bearings are largely made of aluminium. The rear-axle subframe is made of high-strength steel.
The Shooting Brake comes as standard with fully load-bearing air suspension featuring automatic level control at the rear axle. This avoids variations in the compression and rebound strokes and ensures comfortable vibration characteristics even when carrying a full load. In addition, the full ground clearance is maintained at all times.
The spring struts on the front axle consist of cylindrical, lateral force compensating coils springs, dual-pipe shock absorbers and newly-developed three-phase head bearings. The front axle stabiliser is connected to the spring strut, which also assists actively in controlling the front wheels.
The DIRECT CONTROL suspension on the CLS Shooting Brake is equipped as standard with a selective damping system. The shock absorbers adapt to the given driving situation, reducing the damping forces automatically during normal driving with minimal actuation of the shock absorbers and increasing them as necessary up to maximum level during dynamic cornering or evasive manoeuvres. An even sportier suspension set-up is optionally available.
AIRMATIC: air suspension with continuously variable damping system
The optionally available AIRMATIC air suspension (standard on CLS 500 BlueEFFICIENCY/CLS 500 4MATIC BlueEFFICIENCY) is combined with an electronically controlled continuously variable damping system which controls each wheel individually. A total of seven sensors monitor the driving situation and body status and relay information to an electronic control unit which additionally processes information on vehicle speed, steering wheel angle, braking torque and engine torque to determine the ideal shock absorber characteristic. The system adjusts the damping force for each wheel individually according to the given road or driving conditions. The extremely fast damping adjustment enables high driving dynamics without compromising on comfort. In evasive manoeuvres, for example, the damping forces are adapted immediately to the vehicle's driving dynamics. The driver is additionally able to alter the vehicle's characteristic by means of the damping programme switch in a broad range extending from comfortable to sporty handling.
Automatic ride-height control is a feature of the AIRMATIC system. The level of the vehicle does not alter as a result of loading, ensuring that outstanding ride comfort is maintained when the vehicle is loaded. Lowering of the ride height at higher speeds reduces fuel consumption and enhances driving safety. The driver is additionally able to increase ground clearance on rough roads or on difficult upward slopes by pressing the level adjustment button.
Electromechanical Direct-Steer system as on the CLS Coupé
The electromechanical Direct-Steer system, which featured as a world-first in the upper vehicle segment on board the second generation of the CLS Coupé, now graces the Shooting Brake, too. This pioneering innovation offers the engineers broad scope for new tuning options and will be introduced in a large number of Mercedes-Benz models in the coming years. In addition, this steering technology also makes an important contribution to the overall efficiency of the CLS: the steering assist function only requires energy when steering actually takes place, cutting fuel consumption by up to 0.3 litres per 100 km and emissions by 7 g of CO2 per km in comparison to vehicles with hydraulic steering assist.
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 high-strength steel 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.
In combination with the sensors and the control unit, the electromechanical steering system allows substantial degrees of freedom in configuring the forces which the driver is required to apply at the steering wheel in different driving situations – from parking to fast motorway driving. Active damping enhances the feeling of safety when driving straight ahead at high speed. In addition to more precise steering and a more comfortable feel at the wheel, the electromechanical steering system offers a range of additional advantages. Power assistance remains available when the engine is stationary, for example – whereby a control algorithm ensures that the combustion engine is not prompted to start up in ECO start/stop mode when the driver is merely moving the steering wheel while the vehicle is at a standstill. The new steering system has also enabled implementation of the "Active Park Assist" automatic parking function and relieves the strain on the driver on road surfaces which slope away towards the kerb.
The steering system also assists with braking on a surface with vastly varying grip (split friction surface). Sensors recognise the impending yaw (the vehicle starts to turn towards the side of the lane with more grip). Steering-wheel torque is applied to prompt the driver to undertake countersteering. Series of tests conducted with drivers have shown that deploying Steering Assist on split friction surfaces has improved the directional stability and shortened the braking time.
The CLS Shooting Brake comes with a mechanically length and height-adjustable steering column as standard. A variant featuring electric length and height adjustment with easy entry function is optionally available as part of the Memory package. The mechanical and electric versions of the steering column are height-adjustable by +/- 25 mm from the steering wheel's home position and length-adjustable by 15 mm towards the front and 35 mm towards the rear.
Brakes: with Hill-Start Assist and brake drying function
With ADAPTIVE BRAKE, the new CLS offers an innovative braking system incorporating additional assistance functions for even greater comfort and safety. 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 and the ECO start/stop function remains active - 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 already 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 more quickly 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 CLS 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 brake system helps to reduce the unsprung masses through the use of floating (four- and six-cylinder models) or fixed front callipers with housings in aluminium or aluminium composite design and rear floating callipers with aluminium housings. Large front and rear brake discs provide an ideal technical basis for ensuring safe and reliable deceleration in any driving situation. The front and rear discs measure up to 360 millimetres and 320 millimetres in diameter respectively, depending on the engine version. To cool the brakes the Mercedes engineers have developed two-piece aluminium cover plates which have undergone testing in the wind tunnel. These ensure that the cooling air flows from the underbody into the wheel arches and
subsequently on to the brake discs while the vehicle is in motion.
Wheels and tyres: 19-inch size available ex-factory
The four- and six-cylinder variants of the CLS Shooting Brake feature ten-spoke 17-inch light-alloy wheels fitted with 245/45 R 17 tyres as standard. The eight-cylinder models leave the factory with five-spoke 18-inch light-alloy wheels fitted with 255/40 R 18 tyres. Alternatively, 18-inch wheels fitted with tyres in size 255/40 R 18 at the front and 285/35 R 18 at the rear are available for all models. The 19-inch wheels lend the Shooting Brake an even sportier appearance. These wheels are fitted with tyres in size 255/35 R 19 at the front and 285/30 R 19 at the rear.
The electronic stability programme which features as standard also monitors the tyre pressure and displays a warning in case of any sudden loss of pressure in a tyre. For this purpose the system continuously compares the rotational speeds of the wheels, which are primarily dependent on the vehicle's speed, the load and the tyre pressure. The control unit additionally refers to other driving dynamics-related ESP® sensor signals, such as lateral acceleration, yaw rate and wheel torques, in order to diagnose pressure loss in a tyre. In this way the system is able to establish any deviations, informing the driver accordingly on the central display.
CLS 63 AMG: with AMG RIDE CONTROL sports suspension
The suspension, steering and braking system of the CLS 63 AMG Shooting Brake complement the high-tech drive system perfectly. The AMG RIDE CONTROL sports suspension, with steel suspension struts on the front axle and air suspension struts on the rear axle, as well as automatic level control, is enhanced further by an electronically controlled damping system; this automatically adjusts the damping characteristics depending on the driving conditions and reduces the roll angle of the body. The effect of this is lightning-fast adjustment between optimum driving comfort and the best possible agility. The driver can switch between the three suspension modes of "Comfort", "Sport" and "Sport plus" at the press of a button. The 3-stage -ESP® with SPORT Handling mode also enables three individual control strategies to be selected at the press of a button.
The AMG-specific front and rear axles with increased negative camber and optimised elastokinematics help to provide more stability at higher cornering speeds as well as better contact with the road. The front axle, with a track width which is 56 mm wider, is the optimum match for the electromechanical AMG sports parameter steering. It features a more direct ratio, variable power assistance which adapts according to the suspension mode, and also contributes towards reducing fuel consumption since the steering assistance system only draws power when the vehicle is actually being steered.
Perfect deceleration even when driving extremely briskly is provided by the AMG high-performance braking system with 360 mm ventilated and perforated brake discs all-round. Particularly robust, motorsports-tested composite technology is used on the front axle. The optional AMG ceramic high-performance composite braking system with yet larger brake discs and specially painted brake callipers with "AMG Carbon Ceramic" lettering ensures an even higher level of braking performance as well as lower unsprung masses. Good contact with the road, meanwhile, comes courtesy of the titanium grey-painted, high-sheen AMG light-alloy wheels featuring a triple-spoke design and fitted with 255/35 R 19 tyres on the front and 285/30 R 19 tyres on the rear.
Mercedes-Benz CLS Shooting Brake: The Shooting Brake comes as standard with fully load-bearing air suspension featuring automatic level control at the rear axle. This avoids variations in the compression and rebound strokes and ensures comfortable vibration characteristics even when carrying a full load. In addition, the full ground clearance is maintained at all times.