The new Mercedes-Benz CLA-Class: Aerodynamics and All-Round Safety

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V. Aerodynamics: Sleek as they come

With record-breaking aerodynamics, the new CLA-Class combines emotion with efficiency. In respect of its aeroacoustics, i.e. noise level comfort, the four-door coupé is also at the top of its game.

With a Cd value of 0.23, the CLA sets a new benchmark – both within the Mercedes-Benz model range and among all production vehicles. The drag area, Cd x A – which is crucial to aerodynamic resistance – also leads the field, at 0.51 m². The CLA 180 BlueEFFICIENCY Edition, which is due to hit the streets in June, even manages to better this value with its Cd value of 0.22, and when it comes to the drag area, the four-door coupé crosses a magical line with its 0.49 m2. This makes the CLA-Class more streamlined than any other car.

The good air flow characteristics, which are a major contributory factor to the vehicle's low fuel consumption in everyday conditions, result from numerous aerodynamic optimisation measures. These include a low A-pillar shoulder with adapted A-pillar geometry, aerodynamically optimised exterior mirrors, wheel trim designed for low aerodynamic drag or a specially-developed aero light-alloy wheel and serrated wheel spoilers on the front and rear wheel arches.

The patented wheel spoiler was developed with the help of airflow analysis. This seemingly innocuous component reduces undesirable air turbulence in the wheel arches in no less than three ways, by lowering linear turbulence, deflecting the airflow from the wheels and stabilising shear waves with its serrated edge. The wheel spoiler remains effective whatever the suspension level and wheel dimensions.

Extensive underbody panelling, additional panelling in the middle area of the rear axle and an aerodynamically optimised rear silencer followed by a diffuser improve the flow of air under the underbody.

In addition the new CLA offers the lowest level of wind noise in its segment. Numerous measures contribute to make this possible:

- Frameless doors with a multi-stage sealing concept

- The high insulating effect of the side windows

- Form-optimised exterior mirrors

- Exterior noise is also minimised by the reduced height of the A-pillar shoulder

Contribution to active safety: anti-soiling measures

Anti-soiling measures are another aerodynamic discipline – and another area in which aerodynamics specialists at Mercedes-Benz have worked painstakingly on the CLA. Soiling can arise from rain, vehicles travelling ahead and spray thrown up by the vehicle's own wheels. Keeping windows and exterior mirror lenses as clean as possible, and therefore having the best possible visibility under all conditions, makes a contribution to active safety.

In the wind tunnel the aerodynamic specialists optimise components with the help of a fluorescent liquid which makes the soiling clearly visible. The aim is to direct water away so that the side windows and exterior mirror lenses remain clean. This is influenced by the geometry of the A-pillar with its integral components and the geometry of the exterior mirrors and trim strips in the frameless doors.

For example, the side windows: by means of minor geometrical changes of the mirror housings and optimisation in detail, with seals and a special water-capture runnel, soiling has been significantly reduced.

VI. The driving assistance systems: More sophisticated collision warning system as standard

Numerous driving assistance systems offer support in the CLA and reduce the driver's workload. Standard-fit features for the coupé include ATTENTION ASSIST drowsiness detection and radar-based COLLISION PREVENTION ASSIST with adaptive Brake Assist, which now helps to protect the CLA from collisions from a speed of only 7 km/h (previously: over 30 km/h).

The radar-based COLLISION PREVENTION ASSIST system provides the possibly distracted driver with visual and acoustic warnings of identified obstacles and prepares Brake Assist for precision braking. Braking is initiated as soon as the driver steps emphatically on the brake pedal. When an impending danger of collision is identified, COLLISION PREVENTION ASSIST calculates the precise braking force ideally needed to avoid an accident and makes the best possible use of any distance remaining. As a new feature, COLLISION PREVENTION ASSIST affords protection from typical rear-end collisions in dangerous traffic situations in the CLA from a speed of only 7 km/h (previously: over 30 km/h).

COLLISION PREVENTION ASSIST combines with DISTRONIC PLUS to become COLLISION PREVENTION ASSIST PLUS, incorporating an additional function: when a danger of collision persists and the driver fails to respond, the system is able to carry out autonomous braking at speeds of up to 200 km/h, thereby reducing the severity of collisions with slow or stationary vehicles. The system also brakes in response to stationary vehicles at a speed of up to 30 km/h and is able to prevent rear-end collisions at speeds of up to 20 km/h.

Electronic helpers: all the other assistance systems at a glance

Active Parking Assist, which is available as an option for the CLA-Class, has been developed on the basis of the PARKTRONIC system familiar from other model series. Twelve ultrasonic sensors mounted in the front and rear bumpers measure potential longitudinal and transversal parking spaces at the left and right sides of the road. By default the system searches on the right; the turn indicator must be actuated for it to look on the left. Once a suitable space has been identified, the driver stops the vehicle, selects reverse gear and activates the automatic parking assistance system via the controls on the multifunction steering wheel. The system calculates a suitable manoeuvring pattern with a maximum of seven moves to complete the parking operation. The driver is assisted by the automatic actuation of the electromechanical steering during the parking process but still has to operate the accelerator, gearshift and brake. The speed is limited to 10 km/h during the parking process. Parking in spaces situated along slightly curved roads is also supported.

Automatic steering to exit the parking space is a new subfunction. If the vehicle has been parked using Active Parking Assist, the vehicle can be steered out of the longitudinal parking space in which the vehicle had previously been parked. For this the driver has to engage reverse and actuate the turn indicator before activating - via control panel on the multifunction steering wheel - the automatic exit from parking space assistance. Here, too, the driver has to operate the accelerator, brake and gearshift. As soon as the vehicle has assumed a sufficient angle to exit the parking space in one straight move, the wheels are set to the straight ahead position, the process ends and the driver assumes steering control again. The process is completed at the latest when the vehicle is at an angle of 45 degrees relative to the starting position.

A series of further assistance systems can be added to this:

- Adaptive Highbeam Assist: when vehicles are detected ahead of or oncoming to the vehicle, this system automatically dips the beams and adjusts the range of the headlamps appropriate to the distance. The driver benefits from a longer dipped beam range and does not generally need to switch manually between main and dipped beam.

- Blind Spot Assist: detects vehicles in the critical sector by means of two radar sensors located at the sides at the rear of the vehicle. The system warns the driver of the presence of a vehicle by displaying a red triangle in the exterior mirror. If the turn indicator is actuated the red triangle begins to flash and a warning tone is emitted.

- Lane Keeping Assist: a camera behind the windscreen detects carriageway markings and can recognise if the car is about to leave a detected lane unintentionally.

- ATTENTION ASSIST (standard): provides a warning when typical signs of drowsiness are detected. The system's highly sensitive sensors observe the driver's behaviour and can recognise – especially on the basis of how the steering wheel is being moved – if the driver is becoming drowsy or inattentive.

- Speed Limit Assist: a camera fitted behind the windscreen detects speed limit signs at the roadside and compares this data to information contained in the GPS system or the digital map. The relevant speed limit is then displayed in the instrument cluster.

- Brake hold function: when stopping, for example at traffic lights, the driver merely has to press the brake pedal slightly more firmly. They can then take their foot off the brake pedal and the brake will remain engaged until they move off again. The brake is released automatically when the driver steps on the accelerator.

- Hill-Start Assist: this function is able to prevent the vehicle from rolling back unintentionally when moving off on an uphill slope.

- Reversing camera: integrated in the handle strip on the tailgate, the reversing camera features a wide-angle lens. When reverse gear is engaged, the image from the camera is transmitted to the screen of the Audio 20 system or the COMAND system. Static and dynamic guide lines assist the driver during manoeuvring.

- DISTRONIC PLUS: the radar-based adaptive cruise control supports the driver at speeds between zero and 200 km/h by maintaining the distance to the vehicles in front. In doing so it is able to apply the brakes to bring the vehicle to a complete standstill and also accelerate it again. As a result, the system is also particularly convenient in stop-and-go traffic. If the system detects that the distance is being reduced too quickly, it warns the driver with both visual and audible signals.

- Cruise control with SPEEDTRONIC: the cruise control maintains the preset speed. The additional SPEEDTRONIC function ensures that the stored speed is not exceeded. Both functions come as standard with the 7G-DCT dual clutch transmission and are optionally available for the models with manual transmission.

VII. Passive safety: A protection programme for every case

"One star is all you need" – the Mercedes-Benz safety philosophy also applies to the new CLA-Class. Its safety equipment includes belt tensioners and belt force limiters for the rear seats, too, the PRE-SAFE® anticipatory occupant protection system and the active bonnet for pedestrian protection. The line-up also includes seven airbags as standard and the Mercedes automatic emergency call system.

The new CLA-Class has passed the brand's rigorous programme of crash tests. This includes not only some 30 different impact configurations, which are laid down as requirements for safety ratings and international type approval, but also nine proprietary crash tests, such as the roof-drop test or the pole impact test, developed by the brand itself.

The bodyshell structure provides the basis for the high standard of passive safety, both in terms of material and with regard to its structural design. Key features of the front-end structure are the systematic implementation of an available crash length, load distribution over several planes, the new bulkhead and floor concept and the subframe as a deformation element.

A total of three longitudinal member planes – consisting of the straight front longitudinal members with inserted crash boxes made from extruded aluminium box sections, a second, upper plane as prolongation of the load-bearing structure at the A-pillar node in the mirror triangle sector and a third plane at the bottom in front of the subframe – enable the controlled reduction of impact energy.

The subframe provides the torque support for the transverse engine/transmission block and serves to attach the components for the front axle and steering. It consists of several steel plates, some in ultra-high-strength steel, and a hydroformed tube. In order to optimise its deformation properties, the subframe is connected via two aluminium struts leading forward to the aluminium radiator mount located under the front end. In the event of a frontal impact, forces can be discharged at an early juncture into the subframe via this third load path, in order to ensure the best possible energy dissipation.

A plastic crash wedge which is fitted at the rear of the front wheel arches helps to ensure that the wheels do not slide under the front doors in the event of a high-impact crash, irrespective of the turning angles. This means that it will be possible to open the doors, even after a serious accident.

The bulkhead also incorporates a special feature: so-called "skate runners" in front of the two middle longitudinal members discharge forces into the floor. The continuous floor structure consists of a total of four straight longitudinal members. The tunnel roof reinforcements at front and rear combine with the tunnel to provide a further closed profile supporting the front end.

Protection in side-on crashes through controlled deformation

Rigid side structures and defined deformation management help to safeguard the survival space for occupants in the event of a side impact. Elements here include a member fitted diagonally in the rear footwell between centre tunnel and floor side wall which is intended to prevent the floor from being torn open in the event of side impact with a tree.

In the upper sector of the B-pillar high strength steels are used in order to ensure that as little intrusion as possible occurs, and that the passenger cell remains as intact as possible in the event of a side impact. In the lower sector, on the other hand, the B-pillar is designed to be softer, in order to enable energy reduction. In this manner, deformation is directed to a few critical areas beneath the seating surface and transferred to the other vehicle side via the tubular structures in the front seats, transversal members and massive transmission bridge in the main floor.

Extensive pedestrian protection measures including Active Bonnet

The protection of those road users who are most at risk has always been a top priority during the development of Mercedes passenger cars. The new CLA-Class features numerous protective measures designed to help lessen the risk of injury to pedestrians. In order to reduce the loads which arise in the event of a pedestrian impact on the bonnet of the vehicle, the deformation space between the bonnet and the components beneath it has been optimised. This is achieved in part through the appropriate positioning of components such as control units or fluid reservoirs in the engine compartment.

In the CLA-Class an active bonnet is also used. In the event of a pedestrian impact, sophisticated sensors combined with intelligent algorithms trigger actuators in the area of the bonnet hinges. These raise the bonnet by 60 millimetres. The additional space which this creates between the bonnet and the components in the engine compartment means that a head is subject to comparatively low internal acceleration forces on impact.

The deformation characteristics of the bonnet have been developed specifically to meet these requirements. Reductions in the impact loads can be achieved by using aluminium and reinforcing the inside face of the bonnet.

Intelligent restraint systems

The CLA-Class protects its passengers with up to nine airbags. The standard complement comprises driver and front-passenger airbag, a kneebag for the driver, large thorax-pelvisbags incorporated in the seat to protect the chest, stomach and pelvis area and windowbags. The windowbags extend over both rows of seats to the A-pillar triangle. They serve to protect the occupants' heads from hard contact in the event of side impact and can also help to keep limbs inside the vehicle in an accident. The driver and front passenger airbags operate in two stages, according to the expected severity of the impact. The gas generator first of all fills the driver's airbag with 80 and the front passenger's airbag with 60 per cent gas. If a more severe impact is forecast, the second stage of the gas generator will additionally be activated after a delay and the airbags will be filled at a higher pressure level. Sidebags for the rear are optionally available.

The high safety expertise of the CLA-Class's developers is reflected in a host of details. The deformable steering column yields by up to 100 millimetres when the driver exerts pressure on the airbag as a result of forward displacement in an accident, for example. The comfort features also reveal a fine touch: the driver's airbag is connected to a vibration absorber in the steering wheel to reduce vibrations, for example.

Comprehensive precautionary measures in the rear

In developing the new CLA-Class, the Mercedes-Benz safety experts have also attached great importance to the safety of the rear-seat occupants. The new model therefore meets the relevant requirements of the Japanese and Chinese NCAP institutes which also take account of factors such as the ease of use of the rear seat belts. Experts believe that Euro NCAP will extend its rating programme to include rear-seat safety in the medium term. The CLA-Class is already prepared for this and is a role model in this respect – both within and beyond its own vehicle category – with features such as standard-fit belt tensioners and belt force limiters for the outer rear seats. A torsion bar in the roller mechanism twists when the load on it exceeds a defined level. In this way the belt force is limited and with it the load on the seat occupant.

The CLA-Class's features also include the standard-fit ISOFIX child seat securing system on the outer seats. Child seats can additionally be fixed to the vehicle by means of special anchorage points with top tethers.

PRE-SAFE® anticipatory occupant protection

The PRE-SAFE® anticipatory occupant protection system is available in the CLA-Class for the first time as an option. This represents a further step in the ongoing democratisation of this innovation, which was premiered in the S-Class in 2002.

PRE-SAFE® from Mercedes-Benz uses the time between detection of a potential accident situation and a possible collision to initiate preventive protection measures, thus reducing the loads exerted on the occupants in the event of a crash by up to 40 percent.

Core features of PRE-SAFE® are reversible belt tensioning, the closing of side windows and sliding sunroof when critical lateral dynamics are detected and adjustment of the fully electric front passenger seat with memory function to an ideal position for maximum effectiveness of the restraint systems.

PRE-SAFE® is activated when one of the following parameters is met: emergency braking, panic braking, pronounced over- or understeering, critical steering movements or heavy support by adaptive Brake Assist.

Automatic Mercedes-Benz emergency call

In combination with COMAND Online, the new CLA-Class is equipped with the Mercedes-Benz emergency call system. As long as COMAND Online is connected to a mobile phone, the Mercedes-Benz emergency call system can rapidly automatically alert the emergency services in the event of a serious accident.

After the airbags or the pyrotechnical belt tensioners are triggered, the vehicle's exact GPS position and vehicle identification number (VIN) are sent by SMS to a special emergency centre, with positional data also being transmitted using the DTMF method (dual-tone multi-frequency) at the same time. Even if the occupants are unconscious or unsure of exactly where they are because they are on a holiday trip, for example, the emergency services alerted by the emergency centre will be notified quickly with accurate information. The driver can also make the emergency call manually as "MB emergency call" is always the first entry in the system phone directory.

On receiving the call, the emergency centre establishes voice contact with the vehicle occupants in a matter of seconds. A particularly practical aspect in an emergency is that communication takes place not in the language of the country where the accident has occurred but in the language which the driver has preset in COMAND Online.

Other than any mobile phone communication charges, which would only arise in the event of an actual emergency call, no charges are incurred by the driver for the emergency call facility and no contractual relationship – other than the regular mobile phone contract – is required.

Credits: Daimler AG

Copyright © 2013, mercedesgla. All rights reserved.

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The new Mercedes-Benz GLK 2012: Active safety - Assistance systems take the GLK to the top of its market segment

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Assistance systems familiar from the S- and E-Class feature as standard to enable an improvement in active safety and driver-fitness safety and take the compact SUV to the top of its market segment. Electric steering with STEER CONTROL as standard, which supports the driver in unstable driving conditions by triggering an impulse which can be felt on the steering wheel, prompting countersteering by the driver in the correct direction.

Brake Assist (BAS), which provides additional brake power when emergency braking is detected, and ADAPTIVE BRAKE featuring Hill-Start Assist, HOLD function, brake drying in the wet and priming of the brake system when emergency braking is detected all support the driver. The high standard of active safety is ensured by the AGILITY CONTROL suspension with selective damping system, the ESP® Electronic Stability Program with integrated trailer stabilisation and tyre pressure loss warning and, on the 4MATIC models, by permanent all-wheel drive and the 4ETS electronic traction system.

Optional equipment includes the ATTENTION ASSIST drowsiness detection system or the PRE-SAFE® anticipatory safety system. Additional assistance systems, including active variants, are optionally available. One example here is Active Parking Assist, enabling automatic manoeuvring into and out of parking spaces. To facilitate manoeuvring when visibility is poor there is a backup camera with guide lines or – for the first time from Mercedes-Benz – a 360° camera. This feature uses image information from four cameras in the front and rear areas and in the exterior mirror housing to generate a bird's eye view of the vehicle and its surroundings. The undistorted image is presented in real time on the central COMAND display. In addition to the functions of the backup camera, it also enables monitoring of the areas to the side of the vehicle and in front of the vehicle, thus helping to avoid inadvertent collisions during manoeuvring. Guide lines provide additional assistance, the 360° camera marking the vehicle's movement range according to the steering wheel angle.

Additional systems are optionally available as individual items or in special packages. The Driving Assistance package Plus comprises DISTRONIC PLUS including BAS PLUS, PRE-SAFE® Brake, Active Lane Keeping Assist and Active Blind Spot Assist. The Parking package combines the described 360° camera including Active Parking Assist for automatic manoeuvring in and out of parking spaces and PARKTRONIC. The Lane Tracking package includes Lane Keeping Assist and Blind Spot Assist.

The right direction: recommendations from STEER CONTROL

The facelift provides the GLK with electromechanically assisted direct steering. This configuration employs a variable steering ratio which becomes noticeably more direct as the steering wheel angle increases. This provides the driver with better feedback from the road and reduces the necessary steering work. In turn, this results in improved handling and agility. The electric steering system additionally offers speed-sensitive power assistance, providing for enhanced steering comfort throughout the entire speed range.

The standard-fit STEER CONTROL system becomes active when the assistance systems have diagnosed unstable driving conditions which can be alleviated by simple steering movements. To this end, an appropriate level of steering wheel torque is determined on the steering wheel in accordance with the given driving conditions and duly set by the electric steering assist system. In case of oversteering – with the rear end of the vehicle pushing towards the edge of the turn in the road – STEER CONTROL prompts the driver to steer in the opposite direction until the vehicle regains stability. Correspondingly, in case of understeering – with the front end of the vehicle pushing towards the edge of the turn – the driver is prompted to increase the steering wheel angle. The system can also help to compensate yaw when the GLK brakes on a road surface offering different levels of friction on the right and left, e.g. on winter roads which are covered in ice on one side. STEER CONTROL then prompts the driver to turn the steering wheel in the appropriate direction to compensate the yaw.

Even if the driver ignores STEER CONTROL's recommendations, sufficient reserves remain available to stabilise the vehicle with the dynamic handling control systems such as ADAPTIVE BRAKE, ESP® or 4ETS. STEER CONTROL always supports the driver in an "advisory" role, never overruling them.

Stability pact: AGILITY CONTROL – suspension with selective damping system

With the AGILITY CONTROL suspension the GLK demonstrates a high standard of flexibility and is able to resolve the conflict between the different aims pursued in designing SUV suspensions: on the one hand, chassis and suspension engineers seek to create a vehicle which is sporty and agile while at the same time offering a comfortable and soft ride and also performing well on off-road terrain. When the onus is on sporty, adaptive handling, the springs and above all the shock absorbers require a certain hardness. This, in turn, rules out the desired suspension comfort which is typical of the brand and imposes restrictions on off-road capabilities. If the vehicle is fitted with softer dampers in pursuit of suspension comfort and off-road performance, this will naturally diminish the driving dynamics. "Stroke-dependent damping" provides a way out here. The shock absorber is configured such that its cushioning forces are applied in a flexible manner. During normal driving over moderately contoured roads or on slow cross-country trips the system responds in soft mode, to the benefit of the occupants' wellbeing and the vehicle's off-road performance. In order to ensure that this wellbeing is also maintained when the driver adopts a bolder style or in abrupt evasive manoeuvres, the dampers then switch to a harder mode to provide for a high level of driving stability in such situations.

To avoid any unpleasant consequences in the event of tyre damage, all GLK models incorporate a tyre pressure loss warning system. This system detects sudden pressure losses in a tyre and triggers a corresponding warning in the instrument cluster. Tyre pressure monitoring is optionally available to further improve safety in this area. Incorrect tyre pressure or "creeping" pressure losses are indicated by the warning "Check tyres", while rapid pressure losses trigger the message "Caution Tyre malfunction". The tyre pressure monitoring system identifies newly fitted wheels automatically.

"Offroad Engineering package" enables superior off-road performance

The Offroad Engineering package continues to be available, ensuring that the vehicle is well able to assert itself away from paved roads with Downhill Speed Regulation (DSR), off-road driving programme (adaptation of transmission shift points and accelerator characteristic), tough underguard and a raised suspension.

When the "Offroad Engineering package" is on board, the so-called "off-road switch" in the centre console enhances the GLK's capabilities in difficult terrain. At the touch of a button a special drive programme is started which varies the shift points of the 7G-TRONIC, "softens" the accelerator characteristics and activates the ESP® off-road functions with off-road ABS and a special off-road 4ETS system. Engine control intervention is subsequently reduced and the system additionally permits higher wheel slip values. This control strategy improves off-road traction in particular on surfaces offering low friction levels, such as sand, gravel or rubble. The GLK's off-road ABS was premiered in the current M-Class. It identifies the most diverse ground conditions via the continuous comparison of wheel slip models. This results in the best possible deceleration strategies for off-road trips on rock, sand, rubble, gravel or slush.

In this equipment variant with Offroad Engineering package, is provided with a manual drive programme (M) in which the individual gears can be selected via paddles on the multifunction steering wheel. This operating mode guarantees maximum off-road driving enjoyment. An additional switch activates Downhill Speed Regulation (DSR), which automatically maintains a preset speed between 4 and 18 km/h on steep downhill stretches. The driver is able to vary the speed at any time by means of the cruise control lever.

The ground clearance of 210 millimetres and the minimal body overhangs (824 mm at the front, 957 mm at the rear) results in an approach angle of 23 degrees and a departure angle of 25 degrees; the ramp angle stands at 19 degrees. The GLK is able to negotiate gradients of up to 70 percent; the maximum angle of inclination is 35 degrees. Together with the relatively compact wheelbase of 2755 millimetres and the comparatively low vehicle weight, this ensures that the GLK is able to make good progress even in topographically difficult terrain.

Offroad Light for better off-road visibility

When travelling at low speeds in confusing off-road terrain, the broadest and brightest possible illumination of the area in front of the vehicle is expedient to enable more effective and faster recognition of obstacles. As for the GL, a special Offroad Light is thus also available for the new GLK in conjunction with the Offroad Engineering package and the Intelligent Light System (ILS). The Offroad Light goes on automatically when the driver activates the Offroad drive programme while the headlamps are on. To this end, the bi-xenon headlamp modules pan outwards by 6 degrees, the luminous power of the xenon burner is increased by 3 W and a symmetrical light distribution is set. In addition, the LED cornering lights on both sides are switched to permanently lit mode, while dynamic curve illumination and range adjustment are deactivated. These settings ensure broader and brighter illumination of the area directly in front of the vehicle in comparison to ILS, which is optimised for on-road use, enabling any obstacles to be recognised more quickly.

The Offroad Light is active up to a speed of 50 km/h. Upon the driver dropping below this threshold, the ILS automatically reactivates the light functions which are optimised for on-road use.

Credits: Daimler AG

Copyright © 2012, mercedesgla. All rights reserved.

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